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	$73.48	6.833%	$78.5009	$78.50	$78.50	$78.50
Purchase #2	$221.74	10.281%	$244.5371	$244.54	$244.55	$244.50
Purchase #3	$50.46	11.527%	$56.2765	$56.28	$56.30	$56.30
Purchase #4	$135.70	10.547%	$150.0123	$150.01	$150.00	$150.00
Purchase #5	$244.29	11.807%	$273.1333	$273.13	$273.15	$273.10
Purchase #6	$41.90	11.810%	$46.8484	$46.85	$46.85	$46.80
Purchase #7	$96.55	12.795%	$108.9036	$108.90	$108.90	$108.90
7 purchase totals =	$864.12		$958.2121	$958.21	$958.25	$958.10