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 $58.59   9.811%   $64.3383   $64.34   $64.35   $64.30  
  Purchase #2 $118.84   5.863%   $125.8076   $125.81   $125.80   $125.80  
  Purchase #3 $63.37   13.591%   $71.9826   $71.98   $72.00   $72.00  
  Purchase #4 $215.99   10.382%   $238.4141   $238.41   $238.40   $238.40  
  Purchase #5 $68.32   9.370%   $74.7216   $74.72   $74.70   $74.70  
  Purchase #6 $41.39   8.124%   $44.7525   $44.75   $44.75   $44.80  
  Purchase #7 $174.84   10.436%   $193.0863   $193.09   $193.10   $193.10  
  7 purchase totals = $741.34       $813.1030   $813.10   $813.10   $813.10