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	$78.57	12.205%	$88.1595	$88.16	$88.15	$88.20
Purchase #2	$196.85	6.124%	$208.9051	$208.91	$208.90	$208.90
Purchase #3	$152.88	10.317%	$168.6526	$168.65	$168.65	$168.70
Purchase #4	$12.67	13.506%	$14.3812	$14.38	$14.40	$14.40
Purchase #5	$87.89	13.723%	$99.9511	$99.95	$99.95	$100.00
Purchase #6	$78.89	8.776%	$85.8134	$85.81	$85.80	$85.80
Purchase #7	$184.65	11.780%	$206.4018	$206.40	$206.40	$206.40
7 purchase totals =	$792.40		$872.2647	$872.26	$872.25	$872.40