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	$204.29	8.801%	$222.2696	$222.27	$222.25	$222.30
Purchase #2	$164.74	8.453%	$178.6655	$178.67	$178.65	$178.70
Purchase #3	$93.95	12.190%	$105.4025	$105.40	$105.40	$105.40
Purchase #4	$95.64	12.872%	$107.9508	$107.95	$107.95	$108.00
Purchase #5	$29.71	12.667%	$33.4734	$33.47	$33.45	$33.50
Purchase #6	$187.88	11.711%	$209.8826	$209.88	$209.90	$209.90
Purchase #7	$56.30	5.671%	$59.4928	$59.49	$59.50	$59.50
7 purchase totals =	$832.51		$917.1372	$917.13	$917.10	$917.30