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	$111.72	11.264%	$124.3041	$124.30	$124.30	$124.30
Purchase #2	$140.43	8.803%	$152.7921	$152.79	$152.80	$152.80
Purchase #3	$245.35	12.610%	$276.2886	$276.29	$276.30	$276.30
Purchase #4	$98.38	6.539%	$104.8131	$104.81	$104.80	$104.80
Purchase #5	$39.48	7.485%	$42.4351	$42.44	$42.45	$42.40
Purchase #6	$53.51	11.384%	$59.6016	$59.60	$59.60	$59.60
Purchase #7	$123.49	10.749%	$136.7639	$136.76	$136.75	$136.80
7 purchase totals =	$812.36		$896.9985	$896.99	$897.00	$897.00