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	$63.42	13.111%	$71.735	$71.74	$71.75	$71.70
Purchase #2	$149.55	12.261%	$167.8863	$167.89	$167.90	$167.90
Purchase #3	$162.36	3.680%	$168.3348	$168.33	$168.35	$168.30
Purchase #4	$114.55	7.353%	$122.9729	$122.97	$122.95	$123.00
Purchase #5	$185.88	7.180%	$199.2262	$199.23	$199.25	$199.20
Purchase #6	$71.28	9.344%	$77.9404	$77.94	$77.95	$77.90
Purchase #7	$136.52	3.495%	$141.2914	$141.29	$141.30	$141.30
7 purchase totals =	$883.56		$949.3870	$949.39	$949.45	$949.30