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 $61.76   6.719%   $65.9097   $65.91   $65.90   $65.90  
  Purchase #2 $120.32   3.416%   $124.4301   $124.43   $124.45   $124.40  
  Purchase #3 $150.99   6.709%   $161.1199   $161.12   $161.10   $161.10  
  Purchase #4 $21.47   5.202%   $22.5869   $22.59   $22.60   $22.60  
  Purchase #5 $91.67   5.541%   $96.7494   $96.75   $96.75   $96.70  
  Purchase #6 $9.30   7.319%   $9.9807   $9.98   $10.00   $10.00  
  Purchase #7 $197.73   10.116%   $217.7324   $217.73   $217.75   $217.70  
  7 purchase totals = $653.24       $698.5091   $698.51   $698.55   $698.40