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 $231.78   6.623%   $247.1308   $247.13   $247.15   $247.10  
  Purchase #2 $58.58   12.238%   $65.749   $65.75   $65.75   $65.70  
  Purchase #3 $168.95   7.329%   $181.3323   $181.33   $181.35   $181.30  
  Purchase #4 $57.30   12.589%   $64.5135   $64.51   $64.50   $64.50  
  Purchase #5 $242.93   6.351%   $258.3585   $258.36   $258.35   $258.40  
  Purchase #6 $49.34   12.747%   $55.6294   $55.63   $55.65   $55.60  
  Purchase #7 $164.91   13.374%   $186.9651   $186.97   $186.95   $187.00  
  7 purchase totals = $973.79       $1,059.6786   $1,059.68   $1,059.70   $1,059.60