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 $215.84   13.271%   $244.4841   $244.48   $244.50   $244.50  
  Purchase #2 $146.77   9.262%   $160.3638   $160.36   $160.35   $160.40  
  Purchase #3 $24.35   13.655%   $27.675   $27.68   $27.70   $27.70  
  Purchase #4 $192.86   4.289%   $201.1318   $201.13   $201.15   $201.10  
  Purchase #5 $240.93   10.676%   $266.6517   $266.65   $266.65   $266.70  
  Purchase #6 $194.56   9.294%   $212.6424   $212.64   $212.65   $212.60  
  Purchase #7 $185.35   6.839%   $198.0261   $198.03   $198.05   $198.00  
  7 purchase totals = $1,200.66       $1,310.9749   $1,310.97   $1,311.05   $1,311.00