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	$96.34	7.729%	$103.7861	$103.79	$103.80	$103.80
Purchase #2	$25.62	10.447%	$28.2965	$28.30	$28.30	$28.30
Purchase #3	$53.97	11.687%	$60.2775	$60.28	$60.30	$60.30
Purchase #4	$142.57	9.264%	$155.7777	$155.78	$155.80	$155.80
Purchase #5	$9.29	8.795%	$10.1071	$10.11	$10.10	$10.10
Purchase #6	$78.49	6.352%	$83.4757	$83.48	$83.50	$83.50
Purchase #7	$81.54	9.282%	$89.1085	$89.11	$89.10	$89.10
7 purchase totals =	$487.82		$530.8291	$530.85	$530.90	$530.90