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	$86.32	5.507%	$91.0736	$91.07	$91.05	$91.10
Purchase #2	$94.87	4.183%	$98.8384	$98.84	$98.85	$98.80
Purchase #3	$136.73	12.871%	$154.3285	$154.33	$154.35	$154.30
Purchase #4	$67.82	4.240%	$70.6956	$70.70	$70.70	$70.70
Purchase #5	$116.29	9.250%	$127.0468	$127.05	$127.05	$127.00
Purchase #6	$7.61	11.164%	$8.4596	$8.46	$8.45	$8.50
Purchase #7	$137.30	13.490%	$155.8218	$155.82	$155.80	$155.80
7 purchase totals =	$646.94		$706.2643	$706.27	$706.25	$706.20