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 $186.76   5.612%   $197.241   $197.24   $197.25   $197.20  
  Purchase #2 $58.59   12.626%   $65.9876   $65.99   $66.00   $66.00  
  Purchase #3 $209.51   5.646%   $221.3389   $221.34   $221.35   $221.30  
  Purchase #4 $177.72   13.692%   $202.0534   $202.05   $202.05   $202.10  
  Purchase #5 $50.67   5.723%   $53.5698   $53.57   $53.55   $53.60  
  Purchase #6 $62.32   13.532%   $70.7531   $70.75   $70.75   $70.80  
  Purchase #7 $121.30   10.804%   $134.4053   $134.41   $134.40   $134.40  
  7 purchase totals = $866.87       $945.3491   $945.35   $945.35   $945.40