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	$152.54	10.412%	$168.4225	$168.42	$168.40	$168.40
Purchase #2	$239.42	4.520%	$250.2418	$250.24	$250.25	$250.20
Purchase #3	$84.32	7.269%	$90.4492	$90.45	$90.45	$90.40
Purchase #4	$124.34	12.205%	$139.5157	$139.52	$139.50	$139.50
Purchase #5	$22.57	9.191%	$24.6444	$24.64	$24.65	$24.60
Purchase #6	$181.68	7.145%	$194.661	$194.66	$194.65	$194.70
Purchase #7	$152.76	6.292%	$162.3717	$162.37	$162.35	$162.40
7 purchase totals =	$957.63		$1,030.3063	$1,030.30	$1,030.25	$1,030.20