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	$118.56	5.205%	$124.731	$124.73	$124.75	$124.70
Purchase #2	$178.46	7.874%	$192.5119	$192.51	$192.50	$192.50
Purchase #3	$200.85	4.201%	$209.2877	$209.29	$209.30	$209.30
Purchase #4	$152.76	5.298%	$160.8532	$160.85	$160.85	$160.90
Purchase #5	$52.30	6.776%	$55.8438	$55.84	$55.85	$55.80
Purchase #6	$187.77	9.678%	$205.9424	$205.94	$205.95	$205.90
Purchase #7	$127.84	10.806%	$141.6544	$141.65	$141.65	$141.70
7 purchase totals =	$1,018.54		$1,090.8244	$1,090.81	$1,090.85	$1,090.80