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	$208.30	12.479%	$234.2938	$234.29	$234.30	$234.30
Purchase #2	$96.35	13.657%	$109.5085	$109.51	$109.50	$109.50
Purchase #3	$57.69	3.566%	$59.7472	$59.75	$59.75	$59.70
Purchase #4	$73.27	10.318%	$80.83	$80.83	$80.85	$80.80
Purchase #5	$63.66	9.417%	$69.6549	$69.65	$69.65	$69.70
Purchase #6	$230.34	12.286%	$258.6396	$258.64	$258.65	$258.60
Purchase #7	$81.90	12.600%	$92.2194	$92.22	$92.20	$92.20
7 purchase totals =	$811.51		$904.8934	$904.89	$904.90	$904.80