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	$166.79	8.345%	$180.7086	$180.71	$180.70	$180.70
Purchase #2	$84.62	9.410%	$92.5827	$92.58	$92.60	$92.60
Purchase #3	$57.41	6.420%	$61.0957	$61.10	$61.10	$61.10
Purchase #4	$79.64	12.260%	$89.4039	$89.40	$89.40	$89.40
Purchase #5	$55.56	12.595%	$62.5578	$62.56	$62.55	$62.60
Purchase #6	$170.63	4.696%	$178.6428	$178.64	$178.65	$178.60
Purchase #7	$6.75	5.565%	$7.1256	$7.13	$7.15	$7.10
7 purchase totals =	$621.40		$672.1171	$672.12	$672.15	$672.10