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	$233.50	8.740%	$253.9079	$253.91	$253.90	$253.90
Purchase #2	$129.37	11.377%	$144.0884	$144.09	$144.10	$144.10
Purchase #3	$137.88	12.585%	$155.2322	$155.23	$155.25	$155.20
Purchase #4	$87.95	12.122%	$98.6113	$98.61	$98.60	$98.60
Purchase #5	$206.29	8.435%	$223.6906	$223.69	$223.70	$223.70
Purchase #6	$86.59	12.175%	$97.1323	$97.13	$97.15	$97.10
Purchase #7	$243.30	9.172%	$265.6155	$265.62	$265.60	$265.60
7 purchase totals =	$1,124.88		$1,238.2782	$1,238.28	$1,238.30	$1,238.20