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 $71.35   3.228%   $73.6532   $73.65   $73.65   $73.70  
  Purchase #2 $50.98   8.739%   $55.4351   $55.44   $55.45   $55.40  
  Purchase #3 $141.98   3.741%   $147.2915   $147.29   $147.30   $147.30  
  Purchase #4 $163.42   4.791%   $171.2495   $171.25   $171.25   $171.20  
  Purchase #5 $158.71   13.411%   $179.9946   $179.99   $180.00   $180.00  
  Purchase #6 $115.91   5.187%   $121.9223   $121.92   $121.90   $121.90  
  Purchase #7 $8.67   4.541%   $9.0637   $9.06   $9.05   $9.10  
  7 purchase totals = $711.02       $758.6099   $758.60   $758.60   $758.60