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	$235.32	9.142%	$256.833	$256.83	$256.85	$256.80
Purchase #2	$155.39	7.112%	$166.4413	$166.44	$166.45	$166.40
Purchase #3	$248.37	11.349%	$276.5575	$276.56	$276.55	$276.60
Purchase #4	$137.53	12.134%	$154.2179	$154.22	$154.20	$154.20
Purchase #5	$95.90	5.172%	$100.8599	$100.86	$100.85	$100.90
Purchase #6	$73.58	6.310%	$78.2229	$78.22	$78.20	$78.20
Purchase #7	$185.98	5.392%	$196.008	$196.01	$196.00	$196.00
7 purchase totals =	$1,132.07		$1,229.1405	$1,229.14	$1,229.10	$1,229.10