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	$24.61	11.644%	$27.4756	$27.48	$27.50	$27.50
Purchase #2	$75.33	4.599%	$78.7944	$78.79	$78.80	$78.80
Purchase #3	$218.65	7.214%	$234.4234	$234.42	$234.40	$234.40
Purchase #4	$69.38	5.631%	$73.2868	$73.29	$73.30	$73.30
Purchase #5	$149.96	6.263%	$159.352	$159.35	$159.35	$159.40
Purchase #6	$123.88	3.736%	$128.5082	$128.51	$128.50	$128.50
Purchase #7	$180.72	10.127%	$199.0215	$199.02	$199.00	$199.00
7 purchase totals =	$842.53		$900.8619	$900.86	$900.85	$900.90