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	$247.88	7.314%	$266.0099	$266.01	$266.00	$266.00
Purchase #2	$149.68	13.110%	$169.303	$169.30	$169.30	$169.30
Purchase #3	$63.32	6.373%	$67.3554	$67.36	$67.35	$67.40
Purchase #4	$163.62	9.678%	$179.4551	$179.46	$179.45	$179.50
Purchase #5	$18.50	9.376%	$20.2346	$20.23	$20.25	$20.20
Purchase #6	$40.49	5.165%	$42.5813	$42.58	$42.60	$42.60
Purchase #7	$85.89	6.511%	$91.4823	$91.48	$91.50	$91.50
7 purchase totals =	$769.38		$836.4216	$836.42	$836.45	$836.50