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 $135.56   8.188%   $146.6597   $146.66   $146.65   $146.70  
  Purchase #2 $104.98   5.219%   $110.4589   $110.46   $110.45   $110.50  
  Purchase #3 $93.45   7.603%   $100.555   $100.56   $100.55   $100.60  
  Purchase #4 $64.25   7.415%   $69.0141   $69.01   $69.00   $69.00  
  Purchase #5 $139.62   13.616%   $158.6307   $158.63   $158.65   $158.60  
  Purchase #6 $98.71   7.809%   $106.4183   $106.42   $106.40   $106.40  
  Purchase #7 $240.76   9.295%   $263.1386   $263.14   $263.15   $263.10  
  7 purchase totals = $877.33       $954.8753   $954.88   $954.85   $954.90