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	$90.47	3.362%	$93.5116	$93.51	$93.50	$93.50
Purchase #2	$220.55	13.388%	$250.0772	$250.08	$250.10	$250.10
Purchase #3	$19.74	13.384%	$22.382	$22.38	$22.40	$22.40
Purchase #4	$142.34	10.661%	$157.5149	$157.51	$157.50	$157.50
Purchase #5	$106.42	7.738%	$114.6548	$114.65	$114.65	$114.70
Purchase #6	$250.53	5.199%	$263.5551	$263.56	$263.55	$263.60
Purchase #7	$99.59	5.555%	$105.1222	$105.12	$105.10	$105.10
7 purchase totals =	$929.64		$1,006.8178	$1,006.81	$1,006.80	$1,006.90