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	$134.54	5.406%	$141.8132	$141.81	$141.80	$141.80
Purchase #2	$183.42	5.790%	$194.04	$194.04	$194.05	$194.00
Purchase #3	$10.37	5.398%	$10.9298	$10.93	$10.95	$10.90
Purchase #4	$36.35	7.312%	$39.0079	$39.01	$39.00	$39.00
Purchase #5	$141.38	8.553%	$153.4722	$153.47	$153.45	$153.50
Purchase #6	$91.57	8.451%	$99.3086	$99.31	$99.30	$99.30
Purchase #7	$171.54	5.792%	$181.4756	$181.48	$181.50	$181.50
7 purchase totals =	$769.17		$820.0473	$820.05	$820.05	$820.00