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 $156.95   12.354%   $176.3396   $176.34   $176.35   $176.30  
  Purchase #2 $249.74   7.186%   $267.6863   $267.69   $267.70   $267.70  
  Purchase #3 $205.46   7.633%   $221.1428   $221.14   $221.15   $221.10  
  Purchase #4 $86.58   8.713%   $94.1237   $94.12   $94.10   $94.10  
  Purchase #5 $169.45   5.486%   $178.746   $178.75   $178.75   $178.70  
  Purchase #6 $104.81   5.290%   $110.3544   $110.35   $110.35   $110.40  
  Purchase #7 $110.55   11.277%   $123.0167   $123.02   $123.00   $123.00  
  7 purchase totals = $1,083.54       $1,171.4095   $1,171.41   $1,171.40   $1,171.30