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	$249.55	7.117%	$267.3105	$267.31	$267.30	$267.30
Purchase #2	$156.59	5.517%	$165.2291	$165.23	$165.25	$165.20
Purchase #3	$25.39	13.656%	$28.8573	$28.86	$28.85	$28.90
Purchase #4	$74.86	7.745%	$80.6579	$80.66	$80.65	$80.70
Purchase #5	$95.82	3.856%	$99.5148	$99.51	$99.50	$99.50
Purchase #6	$243.59	10.191%	$268.4143	$268.41	$268.40	$268.40
Purchase #7	$31.69	10.182%	$34.9167	$34.92	$34.90	$34.90
7 purchase totals =	$877.49		$944.9006	$944.90	$944.85	$944.90