Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $169.46   7.516%   $182.1966   $182.20   $182.20   $182.20  
  Purchase #2 $203.61   10.153%   $224.2825   $224.28   $224.30   $224.30  
  Purchase #3 $151.81   6.430%   $161.5714   $161.57   $161.55   $161.60  
  Purchase #4 $233.56   6.192%   $248.022   $248.02   $248.00   $248.00  
  Purchase #5 $158.41   12.755%   $178.6152   $178.62   $178.60   $178.60  
  Purchase #6 $130.40   8.500%   $141.484   $141.48   $141.50   $141.50  
  Purchase #7 $119.43   13.871%   $135.9961   $136.00   $136.00   $136.00  
  7 purchase totals = $1,166.68       $1,272.1678   $1,272.17   $1,272.15   $1,272.20