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	$230.33	4.364%	$240.3816	$240.38	$240.40	$240.40
Purchase #2	$41.52	4.865%	$43.5399	$43.54	$43.55	$43.50
Purchase #3	$18.39	5.284%	$19.3617	$19.36	$19.35	$19.40
Purchase #4	$135.58	8.519%	$147.1301	$147.13	$147.15	$147.10
Purchase #5	$103.63	5.603%	$109.4364	$109.44	$109.45	$109.40
Purchase #6	$203.58	13.850%	$231.7758	$231.78	$231.80	$231.80
Purchase #7	$78.83	5.212%	$82.9386	$82.94	$82.95	$82.90
7 purchase totals =	$811.86		$874.5641	$874.57	$874.65	$874.50