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 $242.81   6.123%   $257.6773   $257.68   $257.70   $257.70  
  Purchase #2 $56.85   6.562%   $60.5805   $60.58   $60.60   $60.60  
  Purchase #3 $60.53   7.181%   $64.8767   $64.88   $64.90   $64.90  
  Purchase #4 $53.67   5.125%   $56.4206   $56.42   $56.40   $56.40  
  Purchase #5 $185.93   4.285%   $193.8971   $193.90   $193.90   $193.90  
  Purchase #6 $105.42   5.552%   $111.2729   $111.27   $111.25   $111.30  
  Purchase #7 $27.99   12.140%   $31.388   $31.39   $31.40   $31.40  
  7 purchase totals = $733.20       $776.1131   $776.12   $776.15   $776.20