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	$97.61	12.272%	$109.5887	$109.59	$109.60	$109.60
Purchase #2	$65.38	11.846%	$73.1249	$73.12	$73.10	$73.10
Purchase #3	$91.79	8.719%	$99.7932	$99.79	$99.80	$99.80
Purchase #4	$80.66	6.283%	$85.7279	$85.73	$85.75	$85.70
Purchase #5	$30.56	11.811%	$34.1694	$34.17	$34.15	$34.20
Purchase #6	$216.31	13.490%	$245.4902	$245.49	$245.50	$245.50
Purchase #7	$60.87	4.425%	$63.5635	$63.56	$63.55	$63.60
7 purchase totals =	$643.18		$711.4578	$711.45	$711.45	$711.50