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	$119.64	12.104%	$134.1212	$134.12	$134.10	$134.10
Purchase #2	$29.26	12.187%	$32.8259	$32.83	$32.85	$32.80
Purchase #3	$74.35	8.822%	$80.9092	$80.91	$80.90	$80.90
Purchase #4	$219.72	10.559%	$242.9202	$242.92	$242.90	$242.90
Purchase #5	$7.37	6.123%	$7.8213	$7.82	$7.80	$7.80
Purchase #6	$204.34	7.206%	$219.0647	$219.06	$219.05	$219.10
Purchase #7	$133.89	5.250%	$140.9192	$140.92	$140.90	$140.90
7 purchase totals =	$788.57		$858.5817	$858.58	$858.50	$858.50