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 $51.44   12.299%   $57.7666   $57.77   $57.75   $57.80  
  Purchase #2 $229.96   6.213%   $244.2474   $244.25   $244.25   $244.20  
  Purchase #3 $129.71   12.206%   $145.5424   $145.54   $145.55   $145.50  
  Purchase #4 $202.68   9.667%   $222.2731   $222.27   $222.25   $222.30  
  Purchase #5 $16.78   13.680%   $19.0755   $19.08   $19.10   $19.10  
  Purchase #6 $136.67   9.197%   $149.2395   $149.24   $149.25   $149.20  
  Purchase #7 $213.52   4.216%   $222.522   $222.52   $222.50   $222.50  
  7 purchase totals = $980.76       $1,060.6665   $1,060.67   $1,060.65   $1,060.60