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	$81.36	6.822%	$86.9104	$86.91	$86.90	$86.90
Purchase #2	$135.91	12.522%	$152.9287	$152.93	$152.95	$152.90
Purchase #3	$76.45	11.707%	$85.4	$85.40	$85.40	$85.40
Purchase #4	$231.71	5.690%	$244.8943	$244.89	$244.90	$244.90
Purchase #5	$116.42	12.773%	$131.2903	$131.29	$131.30	$131.30
Purchase #6	$79.77	4.140%	$83.0725	$83.07	$83.05	$83.10
Purchase #7	$125.87	13.401%	$142.7378	$142.74	$142.75	$142.70
7 purchase totals =	$847.49		$927.2340	$927.23	$927.25	$927.20