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	$185.98	4.514%	$194.3751	$194.38	$194.40	$194.40
Purchase #2	$178.82	11.464%	$199.3199	$199.32	$199.30	$199.30
Purchase #3	$221.90	5.851%	$234.8834	$234.88	$234.90	$234.90
Purchase #4	$85.50	6.216%	$90.8147	$90.81	$90.80	$90.80
Purchase #5	$181.82	12.840%	$205.1657	$205.17	$205.15	$205.20
Purchase #6	$242.54	8.398%	$262.9085	$262.91	$262.90	$262.90
Purchase #7	$54.52	4.674%	$57.0683	$57.07	$57.05	$57.10
7 purchase totals =	$1,151.08		$1,244.5356	$1,244.54	$1,244.50	$1,244.60