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 $84.82   12.482%   $95.4072   $95.41   $95.40   $95.40  
  Purchase #2 $70.35   4.749%   $73.6909   $73.69   $73.70   $73.70  
  Purchase #3 $129.48   10.359%   $142.8928   $142.89   $142.90   $142.90  
  Purchase #4 $67.88   8.608%   $73.7231   $73.72   $73.70   $73.70  
  Purchase #5 $215.88   4.319%   $225.2039   $225.20   $225.20   $225.20  
  Purchase #6 $64.48   3.745%   $66.8948   $66.89   $66.90   $66.90  
  Purchase #7 $147.95   4.158%   $154.1018   $154.10   $154.10   $154.10  
  7 purchase totals = $780.84       $831.9145   $831.90   $831.90   $831.90