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	$16.67	7.336%	$17.8929	$17.89	$17.90	$17.90
Purchase #2	$202.29	12.579%	$227.7361	$227.74	$227.75	$227.70
Purchase #3	$147.72	12.595%	$166.3253	$166.33	$166.35	$166.30
Purchase #4	$6.61	12.692%	$7.4489	$7.45	$7.45	$7.40
Purchase #5	$148.62	12.473%	$167.1574	$167.16	$167.15	$167.20
Purchase #6	$82.28	10.701%	$91.0848	$91.08	$91.10	$91.10
Purchase #7	$77.50	6.568%	$82.5902	$82.59	$82.60	$82.60
7 purchase totals =	$681.69		$760.2356	$760.24	$760.30	$760.20