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	$241.26	3.673%	$250.1215	$250.12	$250.10	$250.10
Purchase #2	$127.40	6.584%	$135.788	$135.79	$135.80	$135.80
Purchase #3	$211.53	8.491%	$229.491	$229.49	$229.50	$229.50
Purchase #4	$209.49	6.301%	$222.69	$222.69	$222.70	$222.70
Purchase #5	$149.72	12.717%	$168.7599	$168.76	$168.75	$168.80
Purchase #6	$150.35	9.300%	$164.3326	$164.33	$164.35	$164.30
Purchase #7	$166.81	12.726%	$188.0382	$188.04	$188.05	$188.00
7 purchase totals =	$1,256.56		$1,359.2212	$1,359.22	$1,359.25	$1,359.20