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 $66.37   12.658%   $74.7711   $74.77   $74.75   $74.80  
  Purchase #2 $228.67   6.710%   $244.0138   $244.01   $244.00   $244.00  
  Purchase #3 $250.45   3.552%   $259.346   $259.35   $259.35   $259.30  
  Purchase #4 $205.67   12.690%   $231.7695   $231.77   $231.75   $231.80  
  Purchase #5 $207.62   9.519%   $227.3833   $227.38   $227.40   $227.40  
  Purchase #6 $122.29   11.295%   $136.1027   $136.10   $136.10   $136.10  
  Purchase #7 $213.58   6.748%   $227.9924   $227.99   $228.00   $228.00  
  7 purchase totals = $1,294.65       $1,401.3788   $1,401.37   $1,401.35   $1,401.40