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	$27.73	13.300%	$31.4181	$31.42	$31.40	$31.40
Purchase #2	$104.93	4.334%	$109.4777	$109.48	$109.50	$109.50
Purchase #3	$147.50	11.539%	$164.52	$164.52	$164.50	$164.50
Purchase #4	$32.38	7.222%	$34.7185	$34.72	$34.70	$34.70
Purchase #5	$238.70	3.618%	$247.3362	$247.34	$247.35	$247.30
Purchase #6	$106.32	13.160%	$120.3117	$120.31	$120.30	$120.30
Purchase #7	$57.33	5.210%	$60.3169	$60.32	$60.30	$60.30
7 purchase totals =	$714.89		$768.0991	$768.11	$768.05	$768.00