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	$85.61	3.863%	$88.9171	$88.92	$88.90	$88.90
Purchase #2	$125.65	12.829%	$141.7696	$141.77	$141.75	$141.80
Purchase #3	$32.71	6.652%	$34.8859	$34.89	$34.90	$34.90
Purchase #4	$98.44	11.194%	$109.4594	$109.46	$109.45	$109.50
Purchase #5	$192.44	12.234%	$215.9831	$215.98	$216.00	$216.00
Purchase #6	$130.35	10.483%	$144.0146	$144.01	$144.00	$144.00
Purchase #7	$124.35	13.489%	$141.1236	$141.12	$141.10	$141.10
7 purchase totals =	$789.55		$876.1533	$876.15	$876.10	$876.20