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	$46.91	13.156%	$53.0815	$53.08	$53.10	$53.10
Purchase #2	$93.78	6.285%	$99.6741	$99.67	$99.65	$99.70
Purchase #3	$156.47	8.304%	$169.4633	$169.46	$169.45	$169.50
Purchase #4	$56.78	5.484%	$59.8938	$59.89	$59.90	$59.90
Purchase #5	$108.32	8.437%	$117.459	$117.46	$117.45	$117.50
Purchase #6	$202.48	7.746%	$218.1641	$218.16	$218.15	$218.20
Purchase #7	$111.87	9.569%	$122.5748	$122.57	$122.55	$122.60
7 purchase totals =	$776.61		$840.3106	$840.29	$840.25	$840.50