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	$75.55	7.734%	$81.393	$81.39	$81.40	$81.40
Purchase #2	$180.74	5.266%	$190.2578	$190.26	$190.25	$190.30
Purchase #3	$86.40	5.303%	$90.9818	$90.98	$91.00	$91.00
Purchase #4	$239.81	6.569%	$255.5631	$255.56	$255.55	$255.60
Purchase #5	$224.69	11.497%	$250.5226	$250.52	$250.50	$250.50
Purchase #6	$236.86	11.349%	$263.7412	$263.74	$263.75	$263.70
Purchase #7	$79.88	13.195%	$90.4202	$90.42	$90.40	$90.40
7 purchase totals =	$1,123.93		$1,222.8797	$1,222.87	$1,222.85	$1,222.90