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	$47.75	7.531%	$51.3461	$51.35	$51.35	$51.30
Purchase #2	$82.51	7.394%	$88.6108	$88.61	$88.60	$88.60
Purchase #3	$78.49	8.723%	$85.3367	$85.34	$85.35	$85.30
Purchase #4	$226.61	10.424%	$250.2318	$250.23	$250.25	$250.20
Purchase #5	$219.88	3.519%	$227.6176	$227.62	$227.60	$227.60
Purchase #6	$137.83	13.134%	$155.9326	$155.93	$155.95	$155.90
Purchase #7	$224.64	3.491%	$232.4822	$232.48	$232.50	$232.50
7 purchase totals =	$1,017.71		$1,091.5578	$1,091.56	$1,091.60	$1,091.40