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	$76.45	6.502%	$81.4208	$81.42	$81.40	$81.40
Purchase #2	$61.48	6.138%	$65.2536	$65.25	$65.25	$65.30
Purchase #3	$243.65	6.452%	$259.3703	$259.37	$259.35	$259.40
Purchase #4	$127.46	9.749%	$139.8861	$139.89	$139.90	$139.90
Purchase #5	$50.30	7.221%	$53.9322	$53.93	$53.95	$53.90
Purchase #6	$54.25	11.529%	$60.5045	$60.50	$60.50	$60.50
Purchase #7	$91.34	10.303%	$100.7508	$100.75	$100.75	$100.80
7 purchase totals =	$704.93		$761.1183	$761.11	$761.10	$761.20