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	$83.64	7.766%	$90.1355	$90.14	$90.15	$90.10
Purchase #2	$36.39	11.854%	$40.7037	$40.70	$40.70	$40.70
Purchase #3	$124.81	9.412%	$136.5571	$136.56	$136.55	$136.60
Purchase #4	$137.89	3.796%	$143.1243	$143.12	$143.10	$143.10
Purchase #5	$113.51	10.846%	$125.8213	$125.82	$125.80	$125.80
Purchase #6	$98.66	11.210%	$109.7198	$109.72	$109.70	$109.70
Purchase #7	$16.51	13.202%	$18.6897	$18.69	$18.70	$18.70
7 purchase totals =	$611.41		$664.7514	$664.75	$664.70	$664.70