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	$212.53	11.412%	$236.7839	$236.78	$236.80	$236.80
Purchase #2	$172.58	4.743%	$180.7655	$180.77	$180.75	$180.80
Purchase #3	$243.42	7.473%	$261.6108	$261.61	$261.60	$261.60
Purchase #4	$82.49	4.299%	$86.0362	$86.04	$86.05	$86.00
Purchase #5	$93.89	7.219%	$100.6679	$100.67	$100.65	$100.70
Purchase #6	$39.35	8.625%	$42.7439	$42.74	$42.75	$42.70
Purchase #7	$85.60	4.740%	$89.6574	$89.66	$89.65	$89.70
7 purchase totals =	$929.86		$998.2656	$998.27	$998.25	$998.30