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	$191.30	5.128%	$201.1099	$201.11	$201.10	$201.10
Purchase #2	$136.56	4.460%	$142.6506	$142.65	$142.65	$142.70
Purchase #3	$130.55	9.749%	$143.2773	$143.28	$143.30	$143.30
Purchase #4	$112.55	7.400%	$120.8787	$120.88	$120.90	$120.90
Purchase #5	$50.39	3.448%	$52.1274	$52.13	$52.15	$52.10
Purchase #6	$39.76	7.685%	$42.8156	$42.82	$42.80	$42.80
Purchase #7	$191.67	13.482%	$217.5109	$217.51	$217.50	$217.50
7 purchase totals =	$852.78		$920.3704	$920.38	$920.40	$920.40