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	$167.58	10.267%	$184.7854	$184.79	$184.80	$184.80
Purchase #2	$63.33	4.408%	$66.1216	$66.12	$66.10	$66.10
Purchase #3	$170.43	11.710%	$190.3874	$190.39	$190.40	$190.40
Purchase #4	$41.97	4.459%	$43.8414	$43.84	$43.85	$43.80
Purchase #5	$63.47	10.829%	$70.3432	$70.34	$70.35	$70.30
Purchase #6	$131.78	10.712%	$145.8963	$145.90	$145.90	$145.90
Purchase #7	$159.74	5.662%	$168.7845	$168.78	$168.80	$168.80
7 purchase totals =	$798.30		$870.1598	$870.16	$870.20	$870.10