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 $62.29   9.603%   $68.2717   $68.27   $68.25   $68.30  
  Purchase #2 $237.67   13.341%   $269.3776   $269.38   $269.40   $269.40  
  Purchase #3 $203.69   11.824%   $227.7743   $227.77   $227.75   $227.80  
  Purchase #4 $204.71   10.149%   $225.486   $225.49   $225.50   $225.50  
  Purchase #5 $35.34   3.375%   $36.5327   $36.53   $36.55   $36.50  
  Purchase #6 $200.37   6.351%   $213.0955   $213.10   $213.10   $213.10  
  Purchase #7 $65.84   6.622%   $70.1999   $70.20   $70.20   $70.20  
  7 purchase totals = $1,009.91       $1,110.7377   $1,110.74   $1,110.75   $1,110.80