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 $94.93   12.294%   $106.6007   $106.60   $106.60   $106.60  
  Purchase #2 $55.91   9.676%   $61.3199   $61.32   $61.30   $61.30  
  Purchase #3 $149.37   3.463%   $154.5427   $154.54   $154.55   $154.50  
  Purchase #4 $102.92   10.148%   $113.3643   $113.36   $113.35   $113.40  
  Purchase #5 $212.78   12.748%   $239.9052   $239.91   $239.90   $239.90  
  Purchase #6 $26.80   4.752%   $28.0735   $28.07   $28.05   $28.10  
  Purchase #7 $213.30   8.199%   $230.7885   $230.79   $230.80   $230.80  
  7 purchase totals = $856.01       $934.5948   $934.59   $934.55   $934.60