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 $221.42   6.842%   $236.5696   $236.57   $236.55   $236.60  
  Purchase #2 $49.67   13.186%   $56.2195   $56.22   $56.20   $56.20  
  Purchase #3 $87.94   5.345%   $92.6404   $92.64   $92.65   $92.60  
  Purchase #4 $147.76   13.303%   $167.4165   $167.42   $167.40   $167.40  
  Purchase #5 $177.25   7.333%   $190.2477   $190.25   $190.25   $190.20  
  Purchase #6 $115.48   8.795%   $125.6365   $125.64   $125.65   $125.60  
  Purchase #7 $77.67   6.332%   $82.5881   $82.59   $82.60   $82.60  
  7 purchase totals = $877.19       $951.3183   $951.33   $951.30   $951.20