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	$84.34	5.241%	$88.7603	$88.76	$88.75	$88.80
Purchase #2	$94.58	5.269%	$99.5634	$99.56	$99.55	$99.60
Purchase #3	$20.41	13.294%	$23.1233	$23.12	$23.10	$23.10
Purchase #4	$59.95	10.234%	$66.0853	$66.09	$66.10	$66.10
Purchase #5	$162.79	10.226%	$179.4369	$179.44	$179.45	$179.40
Purchase #6	$92.47	8.499%	$100.329	$100.33	$100.35	$100.30
Purchase #7	$36.46	13.204%	$41.2742	$41.27	$41.25	$41.30
7 purchase totals =	$551.00		$598.5724	$598.57	$598.55	$598.60