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	$96.85	3.617%	$100.3531	$100.35	$100.35	$100.40
Purchase #2	$249.63	11.424%	$278.1477	$278.15	$278.15	$278.10
Purchase #3	$171.56	9.828%	$188.4209	$188.42	$188.40	$188.40
Purchase #4	$141.27	7.832%	$152.3343	$152.33	$152.35	$152.30
Purchase #5	$221.27	9.593%	$242.4964	$242.50	$242.50	$242.50
Purchase #6	$92.83	13.249%	$105.129	$105.13	$105.15	$105.10
Purchase #7	$211.39	7.575%	$227.4028	$227.40	$227.40	$227.40
7 purchase totals =	$1,184.80		$1,294.2842	$1,294.28	$1,294.30	$1,294.20