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 $60.29   9.468%   $65.9983   $66.00   $66.00   $66.00  
  Purchase #2 $237.78   8.193%   $257.2613   $257.26   $257.25   $257.30  
  Purchase #3 $85.61   7.281%   $91.8433   $91.84   $91.85   $91.80  
  Purchase #4 $153.44   10.779%   $169.9793   $169.98   $170.00   $170.00  
  Purchase #5 $32.30   3.295%   $33.3643   $33.36   $33.35   $33.40  
  Purchase #6 $216.40   7.555%   $232.749   $232.75   $232.75   $232.70  
  Purchase #7 $165.61   12.749%   $186.7236   $186.72   $186.70   $186.70  
  7 purchase totals = $951.43       $1,037.9191   $1,037.91   $1,037.90   $1,037.90