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	$71.91	7.426%	$77.25	$77.25	$77.25	$77.30
Purchase #2	$216.50	3.427%	$223.9195	$223.92	$223.90	$223.90
Purchase #3	$77.25	6.181%	$82.0248	$82.02	$82.00	$82.00
Purchase #4	$38.61	7.314%	$41.4339	$41.43	$41.45	$41.40
Purchase #5	$36.54	10.103%	$40.2316	$40.23	$40.25	$40.20
Purchase #6	$49.25	4.346%	$51.3904	$51.39	$51.40	$51.40
Purchase #7	$97.46	9.743%	$106.9555	$106.96	$106.95	$107.00
7 purchase totals =	$587.52		$623.2057	$623.20	$623.20	$623.20