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	$144.48	12.693%	$162.8188	$162.82	$162.80	$162.80
Purchase #2	$89.80	10.198%	$98.9578	$98.96	$98.95	$99.00
Purchase #3	$7.33	7.277%	$7.8634	$7.86	$7.85	$7.90
Purchase #4	$222.55	13.865%	$253.4066	$253.41	$253.40	$253.40
Purchase #5	$155.26	10.337%	$171.3092	$171.31	$171.30	$171.30
Purchase #6	$120.83	7.870%	$130.3393	$130.34	$130.35	$130.30
Purchase #7	$64.25	3.555%	$66.5341	$66.53	$66.55	$66.50
7 purchase totals =	$804.50		$891.2292	$891.23	$891.20	$891.20