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	$15.61	12.576%	$17.5731	$17.57	$17.55	$17.60
Purchase #2	$168.92	6.571%	$180.0197	$180.02	$180.00	$180.00
Purchase #3	$41.69	9.133%	$45.4975	$45.50	$45.50	$45.50
Purchase #4	$173.80	6.319%	$184.7824	$184.78	$184.80	$184.80
Purchase #5	$149.83	11.192%	$166.599	$166.60	$166.60	$166.60
Purchase #6	$233.54	4.441%	$243.9115	$243.91	$243.90	$243.90
Purchase #7	$130.38	5.587%	$137.6643	$137.66	$137.65	$137.70
7 purchase totals =	$913.77		$976.0475	$976.04	$976.00	$976.10