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 $50.38   4.488%   $52.6411   $52.64   $52.65   $52.60  
  Purchase #2 $232.92   8.600%   $252.9511   $252.95   $252.95   $253.00  
  Purchase #3 $210.61   9.157%   $229.8956   $229.90   $229.90   $229.90  
  Purchase #4 $191.63   11.792%   $214.227   $214.23   $214.25   $214.20  
  Purchase #5 $205.29   8.842%   $223.4417   $223.44   $223.45   $223.40  
  Purchase #6 $128.49   12.372%   $144.3868   $144.39   $144.40   $144.40  
  Purchase #7 $115.87   8.719%   $125.9727   $125.97   $125.95   $126.00  
  7 purchase totals = $1,135.19       $1,243.5160   $1,243.52   $1,243.55   $1,243.50