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	$248.84	4.237%	$259.3834	$259.38	$259.40	$259.40
Purchase #2	$197.68	10.333%	$218.1063	$218.11	$218.10	$218.10
Purchase #3	$137.69	6.172%	$146.1882	$146.19	$146.20	$146.20
Purchase #4	$40.96	3.362%	$42.3371	$42.34	$42.35	$42.30
Purchase #5	$92.73	7.587%	$99.7654	$99.77	$99.75	$99.80
Purchase #6	$83.50	3.578%	$86.4876	$86.49	$86.50	$86.50
Purchase #7	$126.42	4.338%	$131.9041	$131.90	$131.90	$131.90
7 purchase totals =	$927.82		$984.1721	$984.18	$984.20	$984.20