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	$190.69	10.381%	$210.4855	$210.49	$210.50	$210.50
Purchase #2	$117.41	8.674%	$127.5941	$127.59	$127.60	$127.60
Purchase #3	$242.47	10.647%	$268.2858	$268.29	$268.30	$268.30
Purchase #4	$205.29	12.558%	$231.0703	$231.07	$231.05	$231.10
Purchase #5	$85.28	13.545%	$96.8312	$96.83	$96.85	$96.80
Purchase #6	$52.47	9.221%	$57.3083	$57.31	$57.30	$57.30
Purchase #7	$89.79	6.148%	$95.3103	$95.31	$95.30	$95.30
7 purchase totals =	$983.40		$1,086.8855	$1,086.89	$1,086.90	$1,086.90