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	$239.34	10.505%	$264.4827	$264.48	$264.50	$264.50
Purchase #2	$73.49	12.777%	$82.8798	$82.88	$82.90	$82.90
Purchase #3	$203.33	7.763%	$219.1145	$219.11	$219.10	$219.10
Purchase #4	$236.54	8.583%	$256.8422	$256.84	$256.85	$256.80
Purchase #5	$134.71	9.431%	$147.4145	$147.41	$147.40	$147.40
Purchase #6	$12.98	12.485%	$14.6006	$14.60	$14.60	$14.60
Purchase #7	$16.81	9.567%	$18.4182	$18.42	$18.40	$18.40
7 purchase totals =	$917.20		$1,003.7525	$1,003.74	$1,003.75	$1,003.70