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 $62.57   7.775%   $67.4348   $67.43   $67.45   $67.40  
  Purchase #2 $184.41   10.819%   $204.3613   $204.36   $204.35   $204.40  
  Purchase #3 $169.45   10.479%   $187.2067   $187.21   $187.20   $187.20  
  Purchase #4 $48.77   5.233%   $51.3221   $51.32   $51.30   $51.30  
  Purchase #5 $23.83   4.708%   $24.9519   $24.95   $24.95   $25.00  
  Purchase #6 $68.85   13.179%   $77.9237   $77.92   $77.90   $77.90  
  Purchase #7 $184.97   3.503%   $191.4495   $191.45   $191.45   $191.40  
  7 purchase totals = $742.85       $804.6500   $804.64   $804.60   $804.60