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	$80.90	10.210%	$89.1599	$89.16	$89.15	$89.20
Purchase #2	$125.83	12.300%	$141.3071	$141.31	$141.30	$141.30
Purchase #3	$96.33	3.472%	$99.6746	$99.67	$99.65	$99.70
Purchase #4	$31.86	12.236%	$35.7584	$35.76	$35.75	$35.80
Purchase #5	$106.51	10.425%	$117.6137	$117.61	$117.60	$117.60
Purchase #6	$30.55	5.515%	$32.2348	$32.23	$32.25	$32.20
Purchase #7	$69.66	4.426%	$72.7432	$72.74	$72.75	$72.70
7 purchase totals =	$541.64		$588.4917	$588.48	$588.45	$588.50