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	$82.78	10.322%	$91.3246	$91.32	$91.30	$91.30
Purchase #2	$144.75	12.435%	$162.7497	$162.75	$162.75	$162.70
Purchase #3	$75.95	9.126%	$82.8812	$82.88	$82.90	$82.90
Purchase #4	$100.71	4.353%	$105.0939	$105.09	$105.10	$105.10
Purchase #5	$65.66	12.529%	$73.8865	$73.89	$73.90	$73.90
Purchase #6	$86.44	13.252%	$97.895	$97.90	$97.90	$97.90
Purchase #7	$13.91	10.167%	$15.3242	$15.32	$15.30	$15.30
7 purchase totals =	$570.20		$629.1551	$629.15	$629.15	$629.10