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 $87.59   12.602%   $98.6281   $98.63   $98.65   $98.60  
  Purchase #2 $126.64   5.547%   $133.6647   $133.66   $133.65   $133.70  
  Purchase #3 $77.49   7.327%   $83.1677   $83.17   $83.15   $83.20  
  Purchase #4 $206.54   9.370%   $225.8928   $225.89   $225.90   $225.90  
  Purchase #5 $72.59   10.816%   $80.4413   $80.44   $80.45   $80.40  
  Purchase #6 $120.84   4.246%   $125.9709   $125.97   $125.95   $126.00  
  Purchase #7 $111.33   4.301%   $116.1183   $116.12   $116.10   $116.10  
  7 purchase totals = $803.02       $863.8838   $863.88   $863.85   $863.90