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 $222.95   9.476%   $244.0767   $244.08   $244.10   $244.10  
  Purchase #2 $15.26   3.451%   $15.7866   $15.79   $15.80   $15.80  
  Purchase #3 $101.26   11.705%   $113.1125   $113.11   $113.10   $113.10  
  Purchase #4 $195.44   5.708%   $206.5957   $206.60   $206.60   $206.60  
  Purchase #5 $73.75   9.127%   $80.4812   $80.48   $80.50   $80.50  
  Purchase #6 $120.42   4.843%   $126.2519   $126.25   $126.25   $126.30  
  Purchase #7 $105.40   3.554%   $109.1459   $109.15   $109.15   $109.10  
  7 purchase totals = $834.48       $895.4505   $895.46   $895.50   $895.50