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 $66.91   11.568%   $74.6501   $74.65   $74.65   $74.70  
  Purchase #2 $217.56   5.332%   $229.1603   $229.16   $229.15   $229.20  
  Purchase #3 $125.45   5.682%   $132.5781   $132.58   $132.60   $132.60  
  Purchase #4 $27.55   12.389%   $30.9632   $30.96   $30.95   $31.00  
  Purchase #5 $242.40   9.659%   $265.8134   $265.81   $265.80   $265.80  
  Purchase #6 $155.51   6.461%   $165.5575   $165.56   $165.55   $165.60  
  Purchase #7 $141.50   8.349%   $153.3138   $153.31   $153.30   $153.30  
  7 purchase totals = $976.88       $1,052.0364   $1,052.03   $1,052.00   $1,052.20