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 $239.55   12.598%   $269.7285   $269.73   $269.75   $269.70  
  Purchase #2 $44.65   3.462%   $46.1958   $46.20   $46.20   $46.20  
  Purchase #3 $87.51   3.501%   $90.5737   $90.57   $90.55   $90.60  
  Purchase #4 $208.26   9.180%   $227.3783   $227.38   $227.40   $227.40  
  Purchase #5 $220.59   12.743%   $248.6998   $248.70   $248.70   $248.70  
  Purchase #6 $37.93   4.603%   $39.6759   $39.68   $39.70   $39.70  
  Purchase #7 $125.28   3.765%   $129.9968   $130.00   $130.00   $130.00  
  7 purchase totals = $963.77       $1,052.2488   $1,052.26   $1,052.30   $1,052.30