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	$180.46	5.518%	$190.4178	$190.42	$190.40	$190.40
Purchase #2	$117.38	5.536%	$123.8782	$123.88	$123.90	$123.90
Purchase #3	$119.88	7.591%	$128.9801	$128.98	$129.00	$129.00
Purchase #4	$191.61	7.774%	$206.5058	$206.51	$206.50	$206.50
Purchase #5	$18.60	4.870%	$19.5058	$19.51	$19.50	$19.50
Purchase #6	$28.91	13.861%	$32.9172	$32.92	$32.90	$32.90
Purchase #7	$119.40	7.165%	$127.955	$127.96	$127.95	$128.00
7 purchase totals =	$776.24		$830.1599	$830.18	$830.15	$830.20