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 $101.79   12.495%   $114.5087   $114.51   $114.50   $114.50  
  Purchase #2 $51.82   5.678%   $54.7623   $54.76   $54.75   $54.80  
  Purchase #3 $112.26   11.705%   $125.4   $125.40   $125.40   $125.40  
  Purchase #4 $109.59   8.222%   $118.6005   $118.60   $118.60   $118.60  
  Purchase #5 $239.42   10.626%   $264.8608   $264.86   $264.85   $264.90  
  Purchase #6 $248.71   12.170%   $278.978   $278.98   $279.00   $279.00  
  Purchase #7 $159.81   3.580%   $165.5312   $165.53   $165.55   $165.50  
  7 purchase totals = $1,023.40       $1,122.6415   $1,122.64   $1,122.65   $1,122.70