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	$6.54	6.769%	$6.9827	$6.98	$7.00	$7.00
Purchase #2	$151.85	5.588%	$160.3354	$160.34	$160.35	$160.30
Purchase #3	$218.58	11.547%	$243.8194	$243.82	$243.80	$243.80
Purchase #4	$104.63	12.410%	$117.6146	$117.61	$117.60	$117.60
Purchase #5	$26.74	5.573%	$28.2302	$28.23	$28.25	$28.20
Purchase #6	$89.51	11.252%	$99.5817	$99.58	$99.60	$99.60
Purchase #7	$75.87	12.122%	$85.067	$85.07	$85.05	$85.10
7 purchase totals =	$673.72		$741.6310	$741.63	$741.65	$741.60