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	$79.74	3.233%	$82.318	$82.32	$82.30	$82.30
Purchase #2	$29.85	10.220%	$32.9007	$32.90	$32.90	$32.90
Purchase #3	$40.52	12.513%	$45.5903	$45.59	$45.60	$45.60
Purchase #4	$40.59	8.793%	$44.1591	$44.16	$44.15	$44.20
Purchase #5	$188.89	8.377%	$204.7133	$204.71	$204.70	$204.70
Purchase #6	$31.85	6.528%	$33.9292	$33.93	$33.95	$33.90
Purchase #7	$65.37	6.502%	$69.6204	$69.62	$69.60	$69.60
7 purchase totals =	$476.81		$513.2310	$513.23	$513.20	$513.20