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 $148.51   11.791%   $166.0208   $166.02   $166.00   $166.00  
  Purchase #2 $53.64   8.788%   $58.3539   $58.35   $58.35   $58.40  
  Purchase #3 $225.68   9.121%   $246.2643   $246.26   $246.25   $246.30  
  Purchase #4 $20.66   9.192%   $22.5591   $22.56   $22.55   $22.60  
  Purchase #5 $109.45   6.106%   $116.133   $116.13   $116.15   $116.10  
  Purchase #6 $76.35   9.159%   $83.3429   $83.34   $83.35   $83.30  
  Purchase #7 $145.74   13.847%   $165.9206   $165.92   $165.90   $165.90  
  7 purchase totals = $780.03       $858.5946   $858.58   $858.55   $858.60