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 $162.34   9.493%   $177.7509   $177.75   $177.75   $177.80  
  Purchase #2 $69.52   9.797%   $76.3309   $76.33   $76.35   $76.30  
  Purchase #3 $117.28   7.605%   $126.1991   $126.20   $126.20   $126.20  
  Purchase #4 $128.73   8.524%   $139.7029   $139.70   $139.70   $139.70  
  Purchase #5 $249.89   8.323%   $270.6883   $270.69   $270.70   $270.70  
  Purchase #6 $113.31   6.707%   $120.9097   $120.91   $120.90   $120.90  
  Purchase #7 $35.93   11.495%   $40.0602   $40.06   $40.05   $40.10  
  7 purchase totals = $877.00       $951.6420   $951.64   $951.65   $951.70