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	$130.92	5.595%	$138.245	$138.25	$138.25	$138.20
Purchase #2	$248.66	9.831%	$273.1058	$273.11	$273.10	$273.10
Purchase #3	$98.83	9.539%	$108.2574	$108.26	$108.25	$108.30
Purchase #4	$229.49	5.839%	$242.8899	$242.89	$242.90	$242.90
Purchase #5	$100.97	5.417%	$106.4395	$106.44	$106.45	$106.40
Purchase #6	$70.87	10.155%	$78.0668	$78.07	$78.05	$78.10
Purchase #7	$97.90	11.662%	$109.3171	$109.32	$109.30	$109.30
7 purchase totals =	$977.64		$1,056.3215	$1,056.34	$1,056.30	$1,056.30