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	$129.83	5.725%	$137.2628	$137.26	$137.25	$137.30
Purchase #2	$33.70	11.489%	$37.5718	$37.57	$37.55	$37.60
Purchase #3	$131.33	7.708%	$141.4529	$141.45	$141.45	$141.50
Purchase #4	$105.40	4.401%	$110.0387	$110.04	$110.05	$110.00
Purchase #5	$229.60	11.207%	$255.3313	$255.33	$255.35	$255.30
Purchase #6	$14.80	11.198%	$16.4573	$16.46	$16.45	$16.50
Purchase #7	$109.56	4.722%	$114.7334	$114.73	$114.75	$114.70
7 purchase totals =	$754.22		$812.8482	$812.84	$812.85	$812.90