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	$70.91	11.683%	$79.1944	$79.19	$79.20	$79.20
Purchase #2	$247.52	8.700%	$269.0542	$269.05	$269.05	$269.10
Purchase #3	$37.75	13.287%	$42.7658	$42.77	$42.75	$42.80
Purchase #4	$136.52	11.666%	$152.4464	$152.45	$152.45	$152.40
Purchase #5	$153.36	11.656%	$171.2356	$171.24	$171.25	$171.20
Purchase #6	$124.92	5.556%	$131.8606	$131.86	$131.85	$131.90
Purchase #7	$53.76	3.202%	$55.4814	$55.48	$55.50	$55.50
7 purchase totals =	$824.74		$902.0384	$902.04	$902.05	$902.10