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 $197.36   12.462%   $221.955   $221.96   $221.95   $222.00  
  Purchase #2 $210.56   13.494%   $238.973   $238.97   $238.95   $239.00  
  Purchase #3 $152.66   13.837%   $173.7836   $173.78   $173.80   $173.80  
  Purchase #4 $112.51   7.517%   $120.9674   $120.97   $120.95   $121.00  
  Purchase #5 $231.67   5.558%   $244.5462   $244.55   $244.55   $244.50  
  Purchase #6 $124.93   11.272%   $139.0121   $139.01   $139.00   $139.00  
  Purchase #7 $117.97   12.350%   $132.5393   $132.54   $132.55   $132.50  
  7 purchase totals = $1,147.66       $1,271.7766   $1,271.78   $1,271.75   $1,271.80