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 $20.79   5.140%   $21.8586   $21.86   $21.85   $21.90  
  Purchase #2 $110.44   13.164%   $124.9783   $124.98   $125.00   $125.00  
  Purchase #3 $130.36   3.358%   $134.7375   $134.74   $134.75   $134.70  
  Purchase #4 $222.58   5.383%   $234.5615   $234.56   $234.55   $234.60  
  Purchase #5 $49.84   12.308%   $55.9743   $55.97   $55.95   $56.00  
  Purchase #6 $110.85   9.756%   $121.6645   $121.66   $121.65   $121.70  
  Purchase #7 $158.88   3.773%   $164.8745   $164.87   $164.85   $164.90  
  7 purchase totals = $803.74       $858.6492   $858.64   $858.60   $858.80