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	$164.29	12.448%	$184.7408	$184.74	$184.75	$184.70
Purchase #2	$101.42	10.375%	$111.9423	$111.94	$111.95	$111.90
Purchase #3	$171.46	13.256%	$194.1887	$194.19	$194.20	$194.20
Purchase #4	$211.67	8.138%	$228.8957	$228.90	$228.90	$228.90
Purchase #5	$201.49	10.817%	$223.2852	$223.29	$223.30	$223.30
Purchase #6	$131.94	11.306%	$146.8571	$146.86	$146.85	$146.90
Purchase #7	$38.68	8.742%	$42.0614	$42.06	$42.05	$42.10
7 purchase totals =	$1,020.95		$1,131.9712	$1,131.98	$1,132.00	$1,132.00