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	$33.91	10.205%	$37.3705	$37.37	$37.35	$37.40
Purchase #2	$244.71	12.518%	$275.3428	$275.34	$275.35	$275.30
Purchase #3	$244.37	11.688%	$272.932	$272.93	$272.95	$272.90
Purchase #4	$67.49	6.841%	$72.107	$72.11	$72.10	$72.10
Purchase #5	$48.49	6.740%	$51.7582	$51.76	$51.75	$51.80
Purchase #6	$108.88	6.711%	$116.1869	$116.19	$116.20	$116.20
Purchase #7	$142.54	12.570%	$160.4573	$160.46	$160.45	$160.50
7 purchase totals =	$890.39		$986.1547	$986.16	$986.15	$986.20