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	$67.94	6.205%	$72.1557	$72.16	$72.15	$72.20
Purchase #2	$13.45	13.174%	$15.2219	$15.22	$15.20	$15.20
Purchase #3	$140.46	8.836%	$152.871	$152.87	$152.85	$152.90
Purchase #4	$230.90	5.450%	$243.4841	$243.48	$243.50	$243.50
Purchase #5	$155.76	4.546%	$162.8408	$162.84	$162.85	$162.80
Purchase #6	$7.33	8.220%	$7.9325	$7.93	$7.95	$7.90
Purchase #7	$97.82	11.379%	$108.9509	$108.95	$108.95	$109.00
7 purchase totals =	$713.66		$763.4569	$763.45	$763.45	$763.50