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 $114.59   4.591%   $119.8508   $119.85   $119.85   $119.90  
  Purchase #2 $201.80   11.181%   $224.3633   $224.36   $224.35   $224.40  
  Purchase #3 $235.25   11.468%   $262.2285   $262.23   $262.25   $262.20  
  Purchase #4 $85.68   12.343%   $96.2555   $96.26   $96.25   $96.30  
  Purchase #5 $30.97   11.717%   $34.5988   $34.60   $34.60   $34.60  
  Purchase #6 $61.53   7.578%   $66.1927   $66.19   $66.20   $66.20  
  Purchase #7 $235.41   6.284%   $250.2032   $250.20   $250.20   $250.20  
  7 purchase totals = $965.23       $1,053.6928   $1,053.69   $1,053.70   $1,053.80