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	$160.48	6.663%	$171.1728	$171.17	$171.15	$171.20
Purchase #2	$72.94	12.536%	$82.0838	$82.08	$82.10	$82.10
Purchase #3	$71.65	8.548%	$77.7746	$77.77	$77.75	$77.80
Purchase #4	$45.60	10.365%	$50.3264	$50.33	$50.35	$50.30
Purchase #5	$102.57	9.498%	$112.3121	$112.31	$112.30	$112.30
Purchase #6	$125.59	12.263%	$140.9911	$140.99	$141.00	$141.00
Purchase #7	$92.69	7.561%	$99.6983	$99.70	$99.70	$99.70
7 purchase totals =	$671.52		$734.3591	$734.35	$734.35	$734.40