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	$100.87	4.473%	$105.3819	$105.38	$105.40	$105.40
Purchase #2	$239.94	4.215%	$250.0535	$250.05	$250.05	$250.10
Purchase #3	$92.55	7.401%	$99.3996	$99.40	$99.40	$99.40
Purchase #4	$63.96	9.565%	$70.0778	$70.08	$70.10	$70.10
Purchase #5	$89.57	5.330%	$94.3441	$94.34	$94.35	$94.30
Purchase #6	$173.47	4.460%	$181.2068	$181.21	$181.20	$181.20
Purchase #7	$229.58	5.554%	$242.3309	$242.33	$242.35	$242.30
7 purchase totals =	$989.94		$1,042.7946	$1,042.79	$1,042.85	$1,042.80