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 $56.76   3.858%   $58.9498   $58.95   $58.95   $58.90  
  Purchase #2 $202.29   3.371%   $209.1092   $209.11   $209.10   $209.10  
  Purchase #3 $26.66   7.325%   $28.6128   $28.61   $28.60   $28.60  
  Purchase #4 $137.47   4.363%   $143.4678   $143.47   $143.45   $143.50  
  Purchase #5 $69.87   6.249%   $74.2362   $74.24   $74.25   $74.20  
  Purchase #6 $20.77   6.525%   $22.1252   $22.13   $22.15   $22.10  
  Purchase #7 $198.67   9.260%   $217.0668   $217.07   $217.05   $217.10  
  7 purchase totals = $712.49       $753.5678   $753.58   $753.55   $753.50