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	$45.99	12.581%	$51.776	$51.78	$51.80	$51.80
Purchase #2	$152.45	4.565%	$159.4093	$159.41	$159.40	$159.40
Purchase #3	$43.67	4.338%	$45.5644	$45.56	$45.55	$45.60
Purchase #4	$180.96	10.214%	$199.4433	$199.44	$199.45	$199.40
Purchase #5	$228.28	8.774%	$248.3093	$248.31	$248.30	$248.30
Purchase #6	$146.59	4.184%	$152.7233	$152.72	$152.70	$152.70
Purchase #7	$10.81	4.665%	$11.3143	$11.31	$11.30	$11.30
7 purchase totals =	$808.75		$868.5399	$868.53	$868.50	$868.50