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	$20.33	7.565%	$21.868	$21.87	$21.85	$21.90
Purchase #2	$30.27	10.829%	$33.5479	$33.55	$33.55	$33.50
Purchase #3	$243.88	13.369%	$276.4843	$276.48	$276.50	$276.50
Purchase #4	$86.75	3.150%	$89.4826	$89.48	$89.50	$89.50
Purchase #5	$222.44	13.825%	$253.1923	$253.19	$253.20	$253.20
Purchase #6	$145.93	8.484%	$158.3107	$158.31	$158.30	$158.30
Purchase #7	$40.57	11.167%	$45.1005	$45.10	$45.10	$45.10
7 purchase totals =	$790.17		$877.9863	$877.98	$878.00	$878.00