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	$77.91	7.469%	$83.7291	$83.73	$83.75	$83.70
Purchase #2	$235.88	12.796%	$266.0632	$266.06	$266.05	$266.10
Purchase #3	$225.53	13.751%	$256.5426	$256.54	$256.55	$256.50
Purchase #4	$149.92	11.595%	$167.3032	$167.30	$167.30	$167.30
Purchase #5	$127.62	7.500%	$137.1915	$137.19	$137.20	$137.20
Purchase #6	$79.72	3.298%	$82.3492	$82.35	$82.35	$82.30
Purchase #7	$160.29	6.854%	$171.2763	$171.28	$171.30	$171.30
7 purchase totals =	$1,056.87		$1,164.4551	$1,164.45	$1,164.50	$1,164.40