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 $68.71   12.678%   $77.4211   $77.42   $77.40   $77.40  
  Purchase #2 $81.79   13.248%   $92.6255   $92.63   $92.65   $92.60  
  Purchase #3 $216.86   7.119%   $232.2983   $232.30   $232.30   $232.30  
  Purchase #4 $247.74   8.649%   $269.167   $269.17   $269.15   $269.20  
  Purchase #5 $188.76   6.317%   $200.684   $200.68   $200.70   $200.70  
  Purchase #6 $222.68   12.228%   $249.9093   $249.91   $249.90   $249.90  
  Purchase #7 $101.39   8.842%   $110.3549   $110.35   $110.35   $110.40  
  7 purchase totals = $1,127.93       $1,232.4601   $1,232.46   $1,232.45   $1,232.50