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	$109.89	8.810%	$119.5713	$119.57	$119.55	$119.60
Purchase #2	$226.73	8.400%	$245.7753	$245.78	$245.80	$245.80
Purchase #3	$96.69	3.805%	$100.3691	$100.37	$100.35	$100.40
Purchase #4	$159.88	9.253%	$174.6737	$174.67	$174.65	$174.70
Purchase #5	$12.54	10.219%	$13.8215	$13.82	$13.80	$13.80
Purchase #6	$174.86	6.315%	$185.9024	$185.90	$185.90	$185.90
Purchase #7	$24.27	9.308%	$26.5291	$26.53	$26.55	$26.50
7 purchase totals =	$804.86		$866.6424	$866.64	$866.60	$866.70