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	$56.53	6.836%	$60.3944	$60.39	$60.40	$60.40
Purchase #2	$187.48	8.334%	$203.1046	$203.10	$203.10	$203.10
Purchase #3	$96.44	4.113%	$100.4066	$100.41	$100.40	$100.40
Purchase #4	$53.72	3.613%	$55.6609	$55.66	$55.65	$55.70
Purchase #5	$135.59	3.438%	$140.2516	$140.25	$140.25	$140.30
Purchase #6	$110.76	9.132%	$120.8746	$120.87	$120.85	$120.90
Purchase #7	$87.70	13.365%	$99.4211	$99.42	$99.40	$99.40
7 purchase totals =	$728.22		$780.1138	$780.10	$780.05	$780.20