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	$136.51	3.211%	$140.8933	$140.89	$140.90	$140.90
Purchase #2	$120.61	4.343%	$125.8481	$125.85	$125.85	$125.80
Purchase #3	$47.89	9.852%	$52.6081	$52.61	$52.60	$52.60
Purchase #4	$67.29	5.696%	$71.1228	$71.12	$71.10	$71.10
Purchase #5	$152.80	12.593%	$172.0421	$172.04	$172.05	$172.00
Purchase #6	$230.86	9.844%	$253.5859	$253.59	$253.60	$253.60
Purchase #7	$60.79	6.414%	$64.6891	$64.69	$64.70	$64.70
7 purchase totals =	$816.75		$880.7894	$880.79	$880.80	$880.70