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 $59.85   10.399%   $66.0738   $66.07   $66.05   $66.10  
  Purchase #2 $229.41   10.532%   $253.5715   $253.57   $253.55   $253.60  
  Purchase #3 $30.73   9.872%   $33.7637   $33.76   $33.75   $33.80  
  Purchase #4 $194.84   4.402%   $203.4169   $203.42   $203.40   $203.40  
  Purchase #5 $6.95   9.160%   $7.5866   $7.59   $7.60   $7.60  
  Purchase #6 $101.59   9.738%   $111.4828   $111.48   $111.50   $111.50  
  Purchase #7 $68.63   10.678%   $75.9583   $75.96   $75.95   $76.00  
  7 purchase totals = $692.00       $751.8536   $751.85   $751.80   $752.00