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	$224.52	8.133%	$242.7802	$242.78	$242.80	$242.80
Purchase #2	$85.60	6.375%	$91.057	$91.06	$91.05	$91.10
Purchase #3	$38.50	11.122%	$42.782	$42.78	$42.80	$42.80
Purchase #4	$76.36	8.290%	$82.6902	$82.69	$82.70	$82.70
Purchase #5	$153.98	3.654%	$159.6064	$159.61	$159.60	$159.60
Purchase #6	$167.58	8.733%	$182.2148	$182.21	$182.20	$182.20
Purchase #7	$13.88	12.786%	$15.6547	$15.65	$15.65	$15.70
7 purchase totals =	$760.42		$816.7853	$816.78	$816.80	$816.90