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 $133.81   13.453%   $151.8115   $151.81   $151.80   $151.80  
  Purchase #2 $120.41   9.321%   $131.6334   $131.63   $131.65   $131.60  
  Purchase #3 $82.37   13.666%   $93.6267   $93.63   $93.65   $93.60  
  Purchase #4 $221.82   12.783%   $250.1753   $250.18   $250.20   $250.20  
  Purchase #5 $60.74   10.174%   $66.9197   $66.92   $66.90   $66.90  
  Purchase #6 $32.95   5.872%   $34.8848   $34.88   $34.90   $34.90  
  Purchase #7 $213.50   5.799%   $225.8809   $225.88   $225.90   $225.90  
  7 purchase totals = $865.60       $954.9323   $954.93   $955.00   $954.90