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 $232.96   13.687%   $264.8452   $264.85   $264.85   $264.80  
  Purchase #2 $60.97   6.541%   $64.958   $64.96   $64.95   $65.00  
  Purchase #3 $129.81   4.243%   $135.3178   $135.32   $135.30   $135.30  
  Purchase #4 $206.64   3.188%   $213.2277   $213.23   $213.25   $213.20  
  Purchase #5 $152.54   7.219%   $163.5519   $163.55   $163.55   $163.60  
  Purchase #6 $69.68   4.428%   $72.7654   $72.77   $72.75   $72.80  
  Purchase #7 $128.72   3.593%   $133.3449   $133.34   $133.35   $133.30  
  7 purchase totals = $981.32       $1,048.0109   $1,048.02   $1,048.00   $1,048.00