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 $222.87   9.598%   $244.2611   $244.26   $244.25   $244.30  
  Purchase #2 $7.26   3.206%   $7.4928   $7.49   $7.50   $7.50  
  Purchase #3 $107.34   6.484%   $114.2999   $114.30   $114.30   $114.30  
  Purchase #4 $209.95   9.347%   $229.574   $229.57   $229.55   $229.60  
  Purchase #5 $242.85   8.125%   $262.5816   $262.58   $262.60   $262.60  
  Purchase #6 $118.47   5.369%   $124.8307   $124.83   $124.85   $124.80  
  Purchase #7 $75.82   12.789%   $85.5166   $85.52   $85.50   $85.50  
  7 purchase totals = $984.56       $1,068.5567   $1,068.55   $1,068.55   $1,068.60