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 $114.82   3.521%   $118.8628   $118.86   $118.85   $118.90  
  Purchase #2 $202.28   5.376%   $213.1546   $213.15   $213.15   $213.20  
  Purchase #3 $248.42   4.739%   $260.1926   $260.19   $260.20   $260.20  
  Purchase #4 $197.39   11.766%   $220.6149   $220.61   $220.60   $220.60  
  Purchase #5 $134.26   9.108%   $146.4884   $146.49   $146.50   $146.50  
  Purchase #6 $187.52   4.666%   $196.2697   $196.27   $196.25   $196.30  
  Purchase #7 $158.70   3.188%   $163.7594   $163.76   $163.75   $163.80  
  7 purchase totals = $1,243.39       $1,319.3424   $1,319.33   $1,319.30   $1,319.50