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 $54.99   7.631%   $59.1863   $59.19   $59.20   $59.20  
  Purchase #2 $151.71   6.777%   $161.9914   $161.99   $162.00   $162.00  
  Purchase #3 $147.39   5.601%   $155.6453   $155.65   $155.65   $155.60  
  Purchase #4 $34.79   3.389%   $35.969   $35.97   $35.95   $36.00  
  Purchase #5 $27.43   12.408%   $30.8335   $30.83   $30.85   $30.80  
  Purchase #6 $101.83   10.485%   $112.5069   $112.51   $112.50   $112.50  
  Purchase #7 $177.63   9.394%   $194.3166   $194.32   $194.30   $194.30  
  7 purchase totals = $695.77       $750.4490   $750.46   $750.45   $750.40