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	$100.97	10.345%	$111.4153	$111.42	$111.40	$111.40
Purchase #2	$67.72	11.295%	$75.369	$75.37	$75.35	$75.40
Purchase #3	$225.52	5.872%	$238.7625	$238.76	$238.75	$238.80
Purchase #4	$121.72	12.675%	$137.148	$137.15	$137.15	$137.10
Purchase #5	$185.80	13.587%	$211.0446	$211.04	$211.05	$211.00
Purchase #6	$6.26	3.143%	$6.4568	$6.46	$6.45	$6.50
Purchase #7	$131.83	13.650%	$149.8248	$149.82	$149.80	$149.80
7 purchase totals =	$839.82		$930.0210	$930.02	$929.95	$930.00