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	$147.85	11.234%	$164.4595	$164.46	$164.45	$164.50
Purchase #2	$47.89	11.673%	$53.4802	$53.48	$53.50	$53.50
Purchase #3	$135.91	9.433%	$148.7304	$148.73	$148.75	$148.70
Purchase #4	$153.83	10.337%	$169.7314	$169.73	$169.75	$169.70
Purchase #5	$170.41	6.549%	$181.5702	$181.57	$181.55	$181.60
Purchase #6	$39.82	13.757%	$45.298	$45.30	$45.30	$45.30
Purchase #7	$144.39	10.717%	$159.8643	$159.86	$159.85	$159.90
7 purchase totals =	$840.10		$923.1340	$923.13	$923.15	$923.20