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 $224.87   4.497%   $234.9824   $234.98   $235.00   $235.00  
  Purchase #2 $158.47   5.155%   $166.6391   $166.64   $166.65   $166.60  
  Purchase #3 $180.74   9.399%   $197.7278   $197.73   $197.75   $197.70  
  Purchase #4 $83.82   8.679%   $91.0947   $91.09   $91.10   $91.10  
  Purchase #5 $55.43   12.479%   $62.3471   $62.35   $62.35   $62.30  
  Purchase #6 $203.38   8.364%   $220.3907   $220.39   $220.40   $220.40  
  Purchase #7 $42.30   3.234%   $43.668   $43.67   $43.65   $43.70  
  7 purchase totals = $949.01       $1,016.8498   $1,016.85   $1,016.90   $1,016.80