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	$91.38	6.490%	$97.3106	$97.31	$97.30	$97.30
Purchase #2	$136.62	3.440%	$141.3197	$141.32	$141.30	$141.30
Purchase #3	$55.38	11.286%	$61.6302	$61.63	$61.65	$61.60
Purchase #4	$73.47	7.131%	$78.7091	$78.71	$78.70	$78.70
Purchase #5	$215.88	10.597%	$238.7568	$238.76	$238.75	$238.80
Purchase #6	$42.40	12.238%	$47.5889	$47.59	$47.60	$47.60
Purchase #7	$157.52	10.563%	$174.1588	$174.16	$174.15	$174.20
7 purchase totals =	$772.65		$839.4741	$839.48	$839.45	$839.50