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	$110.32	9.262%	$120.5378	$120.54	$120.55	$120.50
Purchase #2	$181.42	7.808%	$195.5853	$195.59	$195.60	$195.60
Purchase #3	$81.82	10.619%	$90.5085	$90.51	$90.50	$90.50
Purchase #4	$142.45	9.812%	$156.4272	$156.43	$156.45	$156.40
Purchase #5	$165.44	12.712%	$186.4707	$186.47	$186.45	$186.50
Purchase #6	$60.83	6.507%	$64.7882	$64.79	$64.80	$64.80
Purchase #7	$133.54	13.781%	$151.9431	$151.94	$151.95	$151.90
7 purchase totals =	$875.82		$966.2608	$966.27	$966.30	$966.20