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 $87.90   8.531%   $95.3987   $95.40   $95.40   $95.40  
  Purchase #2 $119.67   3.306%   $123.6263   $123.63   $123.65   $123.60  
  Purchase #3 $153.44   4.594%   $160.489   $160.49   $160.50   $160.50  
  Purchase #4 $223.63   4.160%   $232.933   $232.93   $232.95   $232.90  
  Purchase #5 $80.63   6.319%   $85.725   $85.73   $85.75   $85.70  
  Purchase #6 $180.35   3.219%   $186.1555   $186.16   $186.15   $186.20  
  Purchase #7 $117.78   13.520%   $133.7039   $133.70   $133.70   $133.70  
  7 purchase totals = $963.40       $1,018.0314   $1,018.04   $1,018.10   $1,018.00