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	$29.41	12.111%	$32.9718	$32.97	$32.95	$33.00
Purchase #2	$157.56	12.275%	$176.9005	$176.90	$176.90	$176.90
Purchase #3	$250.42	6.798%	$267.4436	$267.44	$267.45	$267.40
Purchase #4	$241.38	9.143%	$263.4494	$263.45	$263.45	$263.40
Purchase #5	$70.72	11.231%	$78.6626	$78.66	$78.65	$78.70
Purchase #6	$96.92	9.116%	$105.7552	$105.76	$105.75	$105.80
Purchase #7	$57.71	13.775%	$65.6596	$65.66	$65.65	$65.70
7 purchase totals =	$904.12		$990.8427	$990.84	$990.80	$990.90