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 $183.65   10.522%   $202.9737   $202.97   $202.95   $203.00  
  Purchase #2 $12.67   13.668%   $14.4017   $14.40   $14.40   $14.40  
  Purchase #3 $119.70   13.728%   $136.1324   $136.13   $136.15   $136.10  
  Purchase #4 $174.49   3.126%   $179.9446   $179.94   $179.95   $179.90  
  Purchase #5 $241.44   5.289%   $254.2098   $254.21   $254.20   $254.20  
  Purchase #6 $20.75   13.263%   $23.5021   $23.50   $23.50   $23.50  
  Purchase #7 $218.42   11.297%   $243.0949   $243.09   $243.10   $243.10  
  7 purchase totals = $971.12       $1,054.2592   $1,054.24   $1,054.25   $1,054.20