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	$81.25	5.739%	$85.9129	$85.91	$85.90	$85.90
Purchase #2	$82.56	10.287%	$91.0529	$91.05	$91.05	$91.10
Purchase #3	$85.92	6.135%	$91.1912	$91.19	$91.20	$91.20
Purchase #4	$102.31	13.428%	$116.0482	$116.05	$116.05	$116.00
Purchase #5	$128.99	5.603%	$136.2173	$136.22	$136.20	$136.20
Purchase #6	$53.88	11.154%	$59.8898	$59.89	$59.90	$59.90
Purchase #7	$77.54	11.482%	$86.4431	$86.44	$86.45	$86.40
7 purchase totals =	$612.45		$666.7554	$666.75	$666.75	$666.70