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 $62.38   5.821%   $66.0111   $66.01   $66.00   $66.00  
  Purchase #2 $46.67   11.625%   $52.0954   $52.10   $52.10   $52.10  
  Purchase #3 $8.42   7.731%   $9.071   $9.07   $9.05   $9.10  
  Purchase #4 $17.39   6.761%   $18.5657   $18.57   $18.55   $18.60  
  Purchase #5 $140.86   9.628%   $154.422   $154.42   $154.40   $154.40  
  Purchase #6 $29.91   3.710%   $31.0197   $31.02   $31.00   $31.00  
  Purchase #7 $77.26   11.849%   $86.4145   $86.41   $86.40   $86.40  
  7 purchase totals = $382.89       $417.5994   $417.60   $417.50   $417.60