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	$242.57	13.521%	$275.3679	$275.37	$275.35	$275.40
Purchase #2	$191.69	4.616%	$200.5384	$200.54	$200.55	$200.50
Purchase #3	$95.90	3.721%	$99.4684	$99.47	$99.45	$99.50
Purchase #4	$79.73	10.835%	$88.3687	$88.37	$88.35	$88.40
Purchase #5	$163.31	9.201%	$178.3362	$178.34	$178.35	$178.30
Purchase #6	$52.40	9.452%	$57.3528	$57.35	$57.35	$57.40
Purchase #7	$191.77	8.790%	$208.6266	$208.63	$208.65	$208.60
7 purchase totals =	$1,017.37		$1,108.0590	$1,108.07	$1,108.05	$1,108.10