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	$85.59	3.225%	$88.3503	$88.35	$88.35	$88.40
Purchase #2	$85.33	4.666%	$89.3115	$89.31	$89.30	$89.30
Purchase #3	$202.59	5.170%	$213.0639	$213.06	$213.05	$213.10
Purchase #4	$38.34	10.221%	$42.2587	$42.26	$42.25	$42.30
Purchase #5	$223.81	7.194%	$239.9109	$239.91	$239.90	$239.90
Purchase #6	$100.69	13.547%	$114.3305	$114.33	$114.35	$114.30
Purchase #7	$180.63	5.473%	$190.5159	$190.52	$190.50	$190.50
7 purchase totals =	$916.98		$977.7417	$977.74	$977.70	$977.80