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 $83.26   13.868%   $94.8065   $94.81   $94.80   $94.80  
  Purchase #2 $234.77   10.548%   $259.5335   $259.53   $259.55   $259.50  
  Purchase #3 $233.53   11.421%   $260.2015   $260.20   $260.20   $260.20  
  Purchase #4 $61.55   9.218%   $67.2237   $67.22   $67.20   $67.20  
  Purchase #5 $167.26   4.599%   $174.9523   $174.95   $174.95   $175.00  
  Purchase #6 $90.59   8.313%   $98.1207   $98.12   $98.10   $98.10  
  Purchase #7 $237.87   7.754%   $256.3144   $256.31   $256.30   $256.30  
  7 purchase totals = $1,108.83       $1,211.1526   $1,211.14   $1,211.10   $1,211.10