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	$91.56	11.802%	$102.3659	$102.37	$102.35	$102.40
Purchase #2	$54.54	4.753%	$57.1323	$57.13	$57.15	$57.10
Purchase #3	$20.72	5.482%	$21.8559	$21.86	$21.85	$21.90
Purchase #4	$102.69	5.223%	$108.0535	$108.05	$108.05	$108.10
Purchase #5	$135.65	13.440%	$153.8814	$153.88	$153.90	$153.90
Purchase #6	$139.67	9.407%	$152.8088	$152.81	$152.80	$152.80
Purchase #7	$65.31	7.792%	$70.399	$70.40	$70.40	$70.40
7 purchase totals =	$610.14		$666.4968	$666.50	$666.50	$666.60