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	$39.82	3.523%	$41.2229	$41.22	$41.20	$41.20
Purchase #2	$136.74	12.334%	$153.6055	$153.61	$153.60	$153.60
Purchase #3	$56.59	11.582%	$63.1443	$63.14	$63.15	$63.10
Purchase #4	$249.94	11.674%	$279.118	$279.12	$279.10	$279.10
Purchase #5	$130.41	6.627%	$139.0523	$139.05	$139.05	$139.10
Purchase #6	$81.31	6.465%	$86.5667	$86.57	$86.55	$86.60
Purchase #7	$33.45	6.402%	$35.5915	$35.59	$35.60	$35.60
7 purchase totals =	$728.26		$798.3012	$798.30	$798.25	$798.30