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 $111.63   12.851%   $125.9756   $125.98   $126.00   $126.00  
  Purchase #2 $185.72   8.482%   $201.4728   $201.47   $201.45   $201.50  
  Purchase #3 $166.50   4.224%   $173.533   $173.53   $173.55   $173.50  
  Purchase #4 $34.25   8.126%   $37.0332   $37.03   $37.05   $37.00  
  Purchase #5 $182.44   9.515%   $199.7992   $199.80   $199.80   $199.80  
  Purchase #6 $67.31   8.371%   $72.9445   $72.94   $72.95   $72.90  
  Purchase #7 $210.30   3.290%   $217.2189   $217.22   $217.20   $217.20  
  7 purchase totals = $958.15       $1,027.9772   $1,027.97   $1,028.00   $1,027.90