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	$75.94	6.411%	$80.8085	$80.81	$80.80	$80.80
Purchase #2	$35.55	6.435%	$37.8376	$37.84	$37.85	$37.80
Purchase #3	$157.69	8.788%	$171.5478	$171.55	$171.55	$171.50
Purchase #4	$152.61	7.392%	$163.8909	$163.89	$163.90	$163.90
Purchase #5	$40.56	12.753%	$45.7326	$45.73	$45.75	$45.70
Purchase #6	$98.59	13.732%	$112.1284	$112.13	$112.15	$112.10
Purchase #7	$48.91	13.344%	$55.4366	$55.44	$55.45	$55.40
7 purchase totals =	$609.85		$667.3824	$667.39	$667.45	$667.20