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	$164.91	4.504%	$172.3375	$172.34	$172.35	$172.30
Purchase #2	$60.67	10.813%	$67.2302	$67.23	$67.25	$67.20
Purchase #3	$141.63	10.770%	$156.8836	$156.88	$156.90	$156.90
Purchase #4	$69.28	7.286%	$74.3277	$74.33	$74.35	$74.30
Purchase #5	$29.80	12.858%	$33.6317	$33.63	$33.65	$33.60
Purchase #6	$218.79	11.755%	$244.5088	$244.51	$244.50	$244.50
Purchase #7	$73.31	11.302%	$81.5955	$81.60	$81.60	$81.60
7 purchase totals =	$758.39		$830.5150	$830.52	$830.60	$830.40