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 $85.92   12.804%   $96.9212   $96.92   $96.90   $96.90  
  Purchase #2 $215.62   12.575%   $242.7342   $242.73   $242.75   $242.70  
  Purchase #3 $120.71   9.646%   $132.3537   $132.35   $132.35   $132.40  
  Purchase #4 $133.64   7.464%   $143.6149   $143.61   $143.60   $143.60  
  Purchase #5 $242.93   9.765%   $266.6521   $266.65   $266.65   $266.70  
  Purchase #6 $53.70   3.308%   $55.4764   $55.48   $55.50   $55.50  
  Purchase #7 $46.52   7.765%   $50.1323   $50.13   $50.15   $50.10  
  7 purchase totals = $899.04       $987.8848   $987.87   $987.90   $987.90