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 $59.35   13.654%   $67.4536   $67.45   $67.45   $67.50  
  Purchase #2 $110.78   13.227%   $125.4329   $125.43   $125.45   $125.40  
  Purchase #3 $243.71   5.641%   $257.4577   $257.46   $257.45   $257.50  
  Purchase #4 $28.27   7.508%   $30.3925   $30.39   $30.40   $30.40  
  Purchase #5 $71.43   3.574%   $73.9829   $73.98   $74.00   $74.00  
  Purchase #6 $238.40   3.435%   $246.589   $246.59   $246.60   $246.60  
  Purchase #7 $108.33   6.180%   $115.0248   $115.02   $115.00   $115.00  
  7 purchase totals = $860.27       $916.3334   $916.32   $916.35   $916.40