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 $69.86   12.406%   $78.5268   $78.53   $78.55   $78.50  
  Purchase #2 $167.50   11.620%   $186.9635   $186.96   $186.95   $187.00  
  Purchase #3 $171.39   10.831%   $189.9533   $189.95   $189.95   $190.00  
  Purchase #4 $90.74   13.436%   $102.9318   $102.93   $102.95   $102.90  
  Purchase #5 $70.30   5.814%   $74.3872   $74.39   $74.40   $74.40  
  Purchase #6 $163.74   4.330%   $170.8299   $170.83   $170.85   $170.80  
  Purchase #7 $141.86   7.392%   $152.3463   $152.35   $152.35   $152.30  
  7 purchase totals = $875.39       $955.9388   $955.94   $956.00   $955.90