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	$69.55	3.782%	$72.1804	$72.18	$72.20	$72.20
Purchase #2	$103.25	3.408%	$106.7688	$106.77	$106.75	$106.80
Purchase #3	$148.79	6.518%	$158.4881	$158.49	$158.50	$158.50
Purchase #4	$27.72	13.755%	$31.5329	$31.53	$31.55	$31.50
Purchase #5	$40.69	9.466%	$44.5417	$44.54	$44.55	$44.50
Purchase #6	$75.86	6.206%	$80.5679	$80.57	$80.55	$80.60
Purchase #7	$19.91	9.785%	$21.8582	$21.86	$21.85	$21.90
7 purchase totals =	$485.77		$515.9380	$515.94	$515.95	$516.00