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 $242.98   7.218%   $260.5183   $260.52   $260.50   $260.50  
  Purchase #2 $51.97   10.501%   $57.4274   $57.43   $57.45   $57.40  
  Purchase #3 $156.51   12.347%   $175.8343   $175.83   $175.85   $175.80  
  Purchase #4 $158.68   5.315%   $167.1138   $167.11   $167.10   $167.10  
  Purchase #5 $177.80   9.599%   $194.867   $194.87   $194.85   $194.90  
  Purchase #6 $106.76   6.807%   $114.0272   $114.03   $114.05   $114.00  
  Purchase #7 $173.85   12.557%   $195.6803   $195.68   $195.70   $195.70  
  7 purchase totals = $1,068.55       $1,165.4683   $1,165.47   $1,165.50   $1,165.40