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 $59.77   5.661%   $63.1536   $63.15   $63.15   $63.20  
  Purchase #2 $246.72   11.226%   $274.4168   $274.42   $274.40   $274.40  
  Purchase #3 $35.74   9.802%   $39.2432   $39.24   $39.25   $39.20  
  Purchase #4 $96.92   8.781%   $105.4305   $105.43   $105.45   $105.40  
  Purchase #5 $223.94   5.151%   $235.4751   $235.48   $235.50   $235.50  
  Purchase #6 $27.83   5.276%   $29.2983   $29.30   $29.30   $29.30  
  Purchase #7 $35.33   13.754%   $40.1893   $40.19   $40.20   $40.20  
  7 purchase totals = $726.25       $787.2068   $787.21   $787.25   $787.20