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 $118.35   6.494%   $126.0356   $126.04   $126.05   $126.00  
  Purchase #2 $81.38   8.347%   $88.1728   $88.17   $88.15   $88.20  
  Purchase #3 $204.38   9.747%   $224.3009   $224.30   $224.30   $224.30  
  Purchase #4 $239.77   12.864%   $270.614   $270.61   $270.60   $270.60  
  Purchase #5 $200.68   3.799%   $208.3038   $208.30   $208.30   $208.30  
  Purchase #6 $29.93   9.438%   $32.7548   $32.75   $32.75   $32.80  
  Purchase #7 $24.75   6.542%   $26.3691   $26.37   $26.35   $26.40  
  7 purchase totals = $899.24       $976.5510   $976.54   $976.50   $976.60