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	$166.77	6.301%	$177.2782	$177.28	$177.30	$177.30
Purchase #2	$56.25	3.701%	$58.3318	$58.33	$58.35	$58.30
Purchase #3	$78.37	13.762%	$89.1553	$89.16	$89.15	$89.20
Purchase #4	$55.77	9.394%	$61.009	$61.01	$61.00	$61.00
Purchase #5	$227.73	5.196%	$239.5629	$239.56	$239.55	$239.60
Purchase #6	$90.72	13.382%	$102.8602	$102.86	$102.85	$102.90
Purchase #7	$147.70	3.760%	$153.2535	$153.25	$153.25	$153.30
7 purchase totals =	$823.31		$881.4509	$881.45	$881.45	$881.60