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 $92.25   13.124%   $104.3569   $104.36   $104.35   $104.40  
  Purchase #2 $8.94   6.749%   $9.5434   $9.54   $9.55   $9.50  
  Purchase #3 $58.98   9.179%   $64.3938   $64.39   $64.40   $64.40  
  Purchase #4 $241.91   4.199%   $252.0678   $252.07   $252.05   $252.10  
  Purchase #5 $244.60   9.421%   $267.6438   $267.64   $267.65   $267.60  
  Purchase #6 $139.47   5.389%   $146.986   $146.99   $147.00   $147.00  
  Purchase #7 $39.40   13.234%   $44.6142   $44.61   $44.60   $44.60  
  7 purchase totals = $825.55       $889.6059   $889.60   $889.60   $889.60