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	$183.51	3.193%	$189.3695	$189.37	$189.35	$189.40
Purchase #2	$72.49	13.454%	$82.2428	$82.24	$82.25	$82.20
Purchase #3	$206.85	9.224%	$225.9298	$225.93	$225.95	$225.90
Purchase #4	$160.47	12.523%	$180.5657	$180.57	$180.55	$180.60
Purchase #5	$242.93	9.146%	$265.1484	$265.15	$265.15	$265.10
Purchase #6	$232.71	11.359%	$259.1435	$259.14	$259.15	$259.10
Purchase #7	$116.71	12.231%	$130.9848	$130.98	$131.00	$131.00
7 purchase totals =	$1,215.67		$1,333.3845	$1,333.38	$1,333.40	$1,333.30