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 $24.81   4.873%   $26.019   $26.02   $26.00   $26.00  
  Purchase #2 $212.82   8.346%   $230.582   $230.58   $230.60   $230.60  
  Purchase #3 $131.59   13.146%   $148.8888   $148.89   $148.90   $148.90  
  Purchase #4 $249.67   6.379%   $265.5964   $265.60   $265.60   $265.60  
  Purchase #5 $227.77   13.561%   $258.6579   $258.66   $258.65   $258.70  
  Purchase #6 $242.96   9.372%   $265.7302   $265.73   $265.75   $265.70  
  Purchase #7 $183.98   6.223%   $195.4291   $195.43   $195.45   $195.40  
  7 purchase totals = $1,273.60       $1,390.9034   $1,390.91   $1,390.95   $1,390.90