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	$128.41	11.734%	$143.4776	$143.48	$143.50	$143.50
Purchase #2	$27.99	9.285%	$30.5889	$30.59	$30.60	$30.60
Purchase #3	$53.54	10.601%	$59.2158	$59.22	$59.20	$59.20
Purchase #4	$162.77	4.120%	$169.4761	$169.48	$169.50	$169.50
Purchase #5	$201.59	12.449%	$226.6859	$226.69	$226.70	$226.70
Purchase #6	$150.33	10.361%	$165.9057	$165.91	$165.90	$165.90
Purchase #7	$33.38	13.238%	$37.7988	$37.80	$37.80	$37.80
7 purchase totals =	$758.01		$833.1488	$833.17	$833.20	$833.20