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 $241.90   9.486%   $264.8466   $264.85   $264.85   $264.80  
  Purchase #2 $58.96   3.466%   $61.0036   $61.00   $61.00   $61.00  
  Purchase #3 $223.33   7.659%   $240.4348   $240.43   $240.45   $240.40  
  Purchase #4 $85.63   6.566%   $91.2525   $91.25   $91.25   $91.30  
  Purchase #5 $161.28   6.188%   $171.26   $171.26   $171.25   $171.30  
  Purchase #6 $179.25   8.858%   $195.128   $195.13   $195.15   $195.10  
  Purchase #7 $65.66   11.678%   $73.3278   $73.33   $73.35   $73.30  
  7 purchase totals = $1,016.01       $1,097.2533   $1,097.25   $1,097.30   $1,097.20