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	$92.51	7.392%	$99.3483	$99.35	$99.35	$99.30
Purchase #2	$148.42	3.591%	$153.7498	$153.75	$153.75	$153.70
Purchase #3	$147.59	8.588%	$160.265	$160.27	$160.25	$160.30
Purchase #4	$35.50	6.501%	$37.8079	$37.81	$37.80	$37.80
Purchase #5	$128.38	5.869%	$135.9146	$135.91	$135.90	$135.90
Purchase #6	$155.49	10.731%	$172.1756	$172.18	$172.20	$172.20
Purchase #7	$144.42	5.347%	$152.1421	$152.14	$152.15	$152.10
7 purchase totals =	$852.31		$911.4033	$911.41	$911.40	$911.30