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	$87.48	10.115%	$96.3286	$96.33	$96.35	$96.30
Purchase #2	$154.61	8.544%	$167.8199	$167.82	$167.80	$167.80
Purchase #3	$131.81	8.807%	$143.4185	$143.42	$143.40	$143.40
Purchase #4	$80.34	12.150%	$90.1013	$90.10	$90.10	$90.10
Purchase #5	$26.47	3.692%	$27.4473	$27.45	$27.45	$27.40
Purchase #6	$69.70	6.738%	$74.3964	$74.40	$74.40	$74.40
Purchase #7	$19.98	3.753%	$20.7298	$20.73	$20.75	$20.70
7 purchase totals =	$570.39		$620.2418	$620.25	$620.25	$620.10