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	$129.94	5.764%	$137.4297	$137.43	$137.45	$137.40
Purchase #2	$87.91	13.460%	$99.7427	$99.74	$99.75	$99.70
Purchase #3	$198.63	9.153%	$216.8106	$216.81	$216.80	$216.80
Purchase #4	$183.96	3.784%	$190.921	$190.92	$190.90	$190.90
Purchase #5	$130.69	12.815%	$147.4379	$147.44	$147.45	$147.40
Purchase #6	$40.83	11.433%	$45.4981	$45.50	$45.50	$45.50
Purchase #7	$87.64	3.719%	$90.8993	$90.90	$90.90	$90.90
7 purchase totals =	$859.60		$928.7393	$928.74	$928.75	$928.60