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	$125.55	4.578%	$131.2977	$131.30	$131.30	$131.30
Purchase #2	$27.53	9.673%	$30.193	$30.19	$30.20	$30.20
Purchase #3	$156.44	10.454%	$172.7942	$172.79	$172.80	$172.80
Purchase #4	$42.73	6.545%	$45.5267	$45.53	$45.55	$45.50
Purchase #5	$134.89	11.112%	$149.879	$149.88	$149.90	$149.90
Purchase #6	$130.95	8.505%	$142.0873	$142.09	$142.10	$142.10
Purchase #7	$196.80	10.859%	$218.1705	$218.17	$218.15	$218.20
7 purchase totals =	$814.89		$889.9484	$889.95	$890.00	$890.00