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	$168.28	6.598%	$179.3831	$179.38	$179.40	$179.40
Purchase #2	$90.33	9.770%	$99.1552	$99.16	$99.15	$99.20
Purchase #3	$33.68	11.684%	$37.6152	$37.62	$37.60	$37.60
Purchase #4	$102.40	7.792%	$110.379	$110.38	$110.40	$110.40
Purchase #5	$176.87	6.786%	$188.8724	$188.87	$188.85	$188.90
Purchase #6	$44.73	5.776%	$47.3136	$47.31	$47.30	$47.30
Purchase #7	$44.49	9.790%	$48.8456	$48.85	$48.85	$48.80
7 purchase totals =	$660.78		$711.5641	$711.57	$711.55	$711.60