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	$136.77	10.312%	$150.8737	$150.87	$150.85	$150.90
Purchase #2	$45.48	4.233%	$47.4052	$47.41	$47.40	$47.40
Purchase #3	$223.95	13.679%	$254.5841	$254.58	$254.60	$254.60
Purchase #4	$33.27	12.283%	$37.3566	$37.36	$37.35	$37.40
Purchase #5	$52.41	9.721%	$57.5048	$57.50	$57.50	$57.50
Purchase #6	$181.74	13.678%	$206.5984	$206.60	$206.60	$206.60
Purchase #7	$89.62	5.758%	$94.7803	$94.78	$94.80	$94.80
7 purchase totals =	$763.24		$849.1031	$849.10	$849.10	$849.20