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	$250.73	6.273%	$266.4583	$266.46	$266.45	$266.50
Purchase #2	$30.62	12.123%	$34.3321	$34.33	$34.35	$34.30
Purchase #3	$59.74	13.568%	$67.8455	$67.85	$67.85	$67.80
Purchase #4	$147.56	3.330%	$152.4737	$152.47	$152.45	$152.50
Purchase #5	$57.31	12.459%	$64.4503	$64.45	$64.45	$64.50
Purchase #6	$71.43	3.601%	$74.0022	$74.00	$74.00	$74.00
Purchase #7	$51.38	9.704%	$56.3659	$56.37	$56.35	$56.40
7 purchase totals =	$668.77		$715.9280	$715.93	$715.90	$716.00