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 $224.93   6.484%   $239.5145   $239.51   $239.50   $239.50  
  Purchase #2 $244.59   12.444%   $275.0268   $275.03   $275.05   $275.00  
  Purchase #3 $25.99   5.192%   $27.3394   $27.34   $27.35   $27.30  
  Purchase #4 $55.36   11.224%   $61.5736   $61.57   $61.55   $61.60  
  Purchase #5 $92.53   12.396%   $104   $104.00   $104.00   $104.00  
  Purchase #6 $177.82   3.342%   $183.7627   $183.76   $183.75   $183.80  
  Purchase #7 $75.75   11.345%   $84.3438   $84.34   $84.35   $84.30  
  7 purchase totals = $896.97       $975.5608   $975.55   $975.55   $975.50