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	$136.80	4.573%	$143.0559	$143.06	$143.05	$143.10
Purchase #2	$243.89	5.328%	$256.8845	$256.88	$256.90	$256.90
Purchase #3	$91.33	10.654%	$101.0603	$101.06	$101.05	$101.10
Purchase #4	$150.43	8.267%	$162.866	$162.87	$162.85	$162.90
Purchase #5	$231.36	3.740%	$240.0129	$240.01	$240.00	$240.00
Purchase #6	$30.25	7.394%	$32.4867	$32.49	$32.50	$32.50
Purchase #7	$188.77	13.465%	$214.1879	$214.19	$214.20	$214.20
7 purchase totals =	$1,072.83		$1,150.5542	$1,150.56	$1,150.55	$1,150.70