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	$29.33	9.123%	$32.0058	$32.01	$32.00	$32.00
Purchase #2	$35.31	3.580%	$36.5741	$36.57	$36.55	$36.60
Purchase #3	$28.84	11.663%	$32.2036	$32.20	$32.20	$32.20
Purchase #4	$147.72	9.205%	$161.3176	$161.32	$161.30	$161.30
Purchase #5	$210.96	6.533%	$224.742	$224.74	$224.75	$224.70
Purchase #6	$78.71	5.620%	$83.1335	$83.13	$83.15	$83.10
Purchase #7	$18.45	10.707%	$20.4254	$20.43	$20.45	$20.40
7 purchase totals =	$549.32		$590.4020	$590.40	$590.40	$590.30