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 $41.97   13.307%   $47.5549   $47.55   $47.55   $47.60  
  Purchase #2 $91.45   4.531%   $95.5936   $95.59   $95.60   $95.60  
  Purchase #3 $91.46   5.533%   $96.5205   $96.52   $96.50   $96.50  
  Purchase #4 $236.94   5.352%   $249.621   $249.62   $249.60   $249.60  
  Purchase #5 $59.63   3.753%   $61.8679   $61.87   $61.85   $61.90  
  Purchase #6 $81.50   12.870%   $91.9891   $91.99   $92.00   $92.00  
  Purchase #7 $229.66   9.388%   $251.2205   $251.22   $251.20   $251.20  
  7 purchase totals = $832.61       $894.3675   $894.36   $894.30   $894.40