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 $232.99   13.604%   $264.686   $264.69   $264.70   $264.70  
  Purchase #2 $23.95   13.693%   $27.2295   $27.23   $27.25   $27.20  
  Purchase #3 $177.41   12.445%   $199.4887   $199.49   $199.50   $199.50  
  Purchase #4 $9.87   9.248%   $10.7828   $10.78   $10.80   $10.80  
  Purchase #5 $149.68   4.797%   $156.8601   $156.86   $156.85   $156.90  
  Purchase #6 $218.47   8.130%   $236.2316   $236.23   $236.25   $236.20  
  Purchase #7 $205.27   13.379%   $232.7331   $232.73   $232.75   $232.70  
  7 purchase totals = $1,017.64       $1,128.0118   $1,128.01   $1,128.10   $1,128.00