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	$179.37	7.182%	$192.2524	$192.25	$192.25	$192.30
Purchase #2	$39.80	12.608%	$44.818	$44.82	$44.80	$44.80
Purchase #3	$230.82	8.356%	$250.1073	$250.11	$250.10	$250.10
Purchase #4	$106.42	10.665%	$117.7697	$117.77	$117.75	$117.80
Purchase #5	$73.85	11.550%	$82.3797	$82.38	$82.40	$82.40
Purchase #6	$196.95	13.695%	$223.9223	$223.92	$223.90	$223.90
Purchase #7	$189.86	11.689%	$212.0527	$212.05	$212.05	$212.10
7 purchase totals =	$1,017.07		$1,123.3021	$1,123.30	$1,123.25	$1,123.40