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	$142.31	11.741%	$159.0186	$159.02	$159.00	$159.00
Purchase #2	$153.57	11.416%	$171.1016	$171.10	$171.10	$171.10
Purchase #3	$14.41	9.249%	$15.7428	$15.74	$15.75	$15.70
Purchase #4	$97.90	12.257%	$109.8996	$109.90	$109.90	$109.90
Purchase #5	$82.71	10.833%	$91.67	$91.67	$91.65	$91.70
Purchase #6	$150.76	4.727%	$157.8864	$157.89	$157.90	$157.90
Purchase #7	$249.97	9.462%	$273.6222	$273.62	$273.60	$273.60
7 purchase totals =	$891.63		$978.9412	$978.94	$978.90	$978.90