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	$204.34	10.468%	$225.7303	$225.73	$225.75	$225.70
Purchase #2	$153.74	13.344%	$174.2551	$174.26	$174.25	$174.30
Purchase #3	$129.85	13.508%	$147.3901	$147.39	$147.40	$147.40
Purchase #4	$162.35	5.799%	$171.7647	$171.76	$171.75	$171.80
Purchase #5	$76.50	13.771%	$87.0348	$87.03	$87.05	$87.00
Purchase #6	$73.84	12.123%	$82.7916	$82.79	$82.80	$82.80
Purchase #7	$79.58	12.473%	$89.506	$89.51	$89.50	$89.50
7 purchase totals =	$880.20		$978.4726	$978.47	$978.50	$978.50