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	$239.88	8.688%	$260.7208	$260.72	$260.70	$260.70
Purchase #2	$149.76	10.514%	$165.5058	$165.51	$165.50	$165.50
Purchase #3	$87.94	5.240%	$92.5481	$92.55	$92.55	$92.50
Purchase #4	$94.62	11.598%	$105.594	$105.59	$105.60	$105.60
Purchase #5	$62.41	12.356%	$70.1214	$70.12	$70.10	$70.10
Purchase #6	$171.48	8.191%	$185.5259	$185.53	$185.55	$185.50
Purchase #7	$155.89	8.309%	$168.8429	$168.84	$168.85	$168.80
7 purchase totals =	$961.98		$1,048.8589	$1,048.86	$1,048.85	$1,048.70