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 $242.69   11.157%   $269.7669   $269.77   $269.75   $269.80  
  Purchase #2 $227.72   13.359%   $258.1411   $258.14   $258.15   $258.10  
  Purchase #3 $230.40   6.505%   $245.3875   $245.39   $245.40   $245.40  
  Purchase #4 $238.73   5.146%   $251.015   $251.02   $251.00   $251.00  
  Purchase #5 $133.32   5.356%   $140.4606   $140.46   $140.45   $140.50  
  Purchase #6 $121.79   8.821%   $132.5331   $132.53   $132.55   $132.50  
  Purchase #7 $240.72   12.616%   $271.0892   $271.09   $271.10   $271.10  
  7 purchase totals = $1,435.37       $1,568.3934   $1,568.40   $1,568.40   $1,568.40