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 $42.97   11.724%   $48.0078   $48.01   $48.00   $48.00  
  Purchase #2 $116.61   12.675%   $131.3903   $131.39   $131.40   $131.40  
  Purchase #3 $166.73   11.781%   $186.3725   $186.37   $186.35   $186.40  
  Purchase #4 $159.99   6.461%   $170.327   $170.33   $170.35   $170.30  
  Purchase #5 $218.75   6.367%   $232.6778   $232.68   $232.70   $232.70  
  Purchase #6 $173.61   12.691%   $195.6428   $195.64   $195.65   $195.60  
  Purchase #7 $56.46   4.361%   $58.9222   $58.92   $58.90   $58.90  
  7 purchase totals = $935.12       $1,023.3404   $1,023.34   $1,023.35   $1,023.30