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	$185.28	12.538%	$208.5104	$208.51	$208.50	$208.50
Purchase #2	$56.58	5.791%	$59.8565	$59.86	$59.85	$59.90
Purchase #3	$240.76	11.528%	$268.5148	$268.51	$268.50	$268.50
Purchase #4	$127.79	7.483%	$137.3525	$137.35	$137.35	$137.40
Purchase #5	$93.83	4.838%	$98.3695	$98.37	$98.35	$98.40
Purchase #6	$129.48	8.755%	$140.816	$140.82	$140.80	$140.80
Purchase #7	$41.26	4.590%	$43.1538	$43.15	$43.15	$43.20
7 purchase totals =	$874.98		$956.5735	$956.57	$956.50	$956.70