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	$131.62	5.707%	$139.1316	$139.13	$139.15	$139.10
Purchase #2	$144.29	4.742%	$151.1322	$151.13	$151.15	$151.10
Purchase #3	$48.68	8.154%	$52.6494	$52.65	$52.65	$52.60
Purchase #4	$80.56	11.231%	$89.6077	$89.61	$89.60	$89.60
Purchase #5	$157.82	8.654%	$171.4777	$171.48	$171.50	$171.50
Purchase #6	$120.39	12.413%	$135.334	$135.33	$135.35	$135.30
Purchase #7	$135.65	12.357%	$152.4123	$152.41	$152.40	$152.40
7 purchase totals =	$819.01		$891.7449	$891.74	$891.80	$891.60