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 $185.98   11.606%   $207.5648   $207.56   $207.55   $207.60  
  Purchase #2 $222.37   11.146%   $247.1554   $247.16   $247.15   $247.20  
  Purchase #3 $177.68   6.735%   $189.6467   $189.65   $189.65   $189.60  
  Purchase #4 $235.27   11.573%   $262.4978   $262.50   $262.50   $262.50  
  Purchase #5 $40.55   8.125%   $43.8447   $43.84   $43.85   $43.80  
  Purchase #6 $229.45   4.670%   $240.1653   $240.17   $240.15   $240.20  
  Purchase #7 $232.85   9.804%   $255.6786   $255.68   $255.70   $255.70  
  7 purchase totals = $1,324.15       $1,446.5533   $1,446.56   $1,446.55   $1,446.60