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 $227.86   6.171%   $241.9212   $241.92   $241.90   $241.90  
  Purchase #2 $70.86   5.445%   $74.7183   $74.72   $74.70   $74.70  
  Purchase #3 $154.84   13.475%   $175.7047   $175.70   $175.70   $175.70  
  Purchase #4 $45.54   10.822%   $50.4683   $50.47   $50.45   $50.50  
  Purchase #5 $47.53   9.484%   $52.0377   $52.04   $52.05   $52.00  
  Purchase #6 $103.73   6.757%   $110.739   $110.74   $110.75   $110.70  
  Purchase #7 $143.90   3.755%   $149.3034   $149.30   $149.30   $149.30  
  7 purchase totals = $794.26       $854.8926   $854.89   $854.85   $854.80