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	$135.72	6.188%	$144.1184	$144.12	$144.10	$144.10
Purchase #2	$126.51	12.272%	$142.0353	$142.04	$142.05	$142.00
Purchase #3	$202.46	10.534%	$223.7871	$223.79	$223.80	$223.80
Purchase #4	$210.34	12.379%	$236.378	$236.38	$236.40	$236.40
Purchase #5	$170.39	5.580%	$179.8978	$179.90	$179.90	$179.90
Purchase #6	$52.54	8.256%	$56.8777	$56.88	$56.90	$56.90
Purchase #7	$240.94	12.228%	$270.4021	$270.40	$270.40	$270.40
7 purchase totals =	$1,138.90		$1,253.4964	$1,253.51	$1,253.55	$1,253.50