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	$12.45	8.500%	$13.5083	$13.51	$13.50	$13.50
Purchase #2	$118.90	3.790%	$123.4063	$123.41	$123.40	$123.40
Purchase #3	$81.34	12.556%	$91.5531	$91.55	$91.55	$91.60
Purchase #4	$93.91	6.866%	$100.3579	$100.36	$100.35	$100.40
Purchase #5	$135.42	10.412%	$149.5199	$149.52	$149.50	$149.50
Purchase #6	$14.88	3.302%	$15.3713	$15.37	$15.35	$15.40
Purchase #7	$221.92	8.249%	$240.2262	$240.23	$240.25	$240.20
7 purchase totals =	$678.82		$733.9430	$733.95	$733.90	$734.00