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 $61.74   13.286%   $69.9428   $69.94   $69.95   $69.90  
  Purchase #2 $131.75   8.151%   $142.4889   $142.49   $142.50   $142.50  
  Purchase #3 $185.34   9.851%   $203.5978   $203.60   $203.60   $203.60  
  Purchase #4 $25.32   9.845%   $27.8128   $27.81   $27.80   $27.80  
  Purchase #5 $187.25   6.272%   $198.9943   $198.99   $199.00   $199.00  
  Purchase #6 $10.84   12.274%   $12.1705   $12.17   $12.15   $12.20  
  Purchase #7 $215.28   11.761%   $240.5991   $240.60   $240.60   $240.60  
  7 purchase totals = $817.52       $895.6062   $895.60   $895.60   $895.60