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	$31.68	7.708%	$34.1219	$34.12	$34.10	$34.10
Purchase #2	$43.50	4.228%	$45.3392	$45.34	$45.35	$45.30
Purchase #3	$152.75	10.306%	$168.4924	$168.49	$168.50	$168.50
Purchase #4	$40.90	11.805%	$45.7282	$45.73	$45.75	$45.70
Purchase #5	$10.56	7.477%	$11.3496	$11.35	$11.35	$11.30
Purchase #6	$62.40	5.844%	$66.0467	$66.05	$66.05	$66.00
Purchase #7	$65.36	12.372%	$73.4463	$73.45	$73.45	$73.40
7 purchase totals =	$407.15		$444.5243	$444.53	$444.55	$444.30