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	$80.43	12.383%	$90.3896	$90.39	$90.40	$90.40
Purchase #2	$71.59	10.222%	$78.9079	$78.91	$78.90	$78.90
Purchase #3	$240.46	12.227%	$269.861	$269.86	$269.85	$269.90
Purchase #4	$181.78	9.595%	$199.2218	$199.22	$199.20	$199.20
Purchase #5	$167.33	8.776%	$182.0149	$182.01	$182.00	$182.00
Purchase #6	$229.25	13.804%	$260.8957	$260.90	$260.90	$260.90
Purchase #7	$224.63	7.649%	$241.8119	$241.81	$241.80	$241.80
7 purchase totals =	$1,195.47		$1,323.1028	$1,323.10	$1,323.05	$1,323.10