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	$37.67	9.345%	$41.1903	$41.19	$41.20	$41.20
Purchase #2	$78.48	13.753%	$89.2734	$89.27	$89.25	$89.30
Purchase #3	$141.96	12.682%	$159.9634	$159.96	$159.95	$160.00
Purchase #4	$159.75	11.796%	$178.5941	$178.59	$178.60	$178.60
Purchase #5	$142.42	9.453%	$155.883	$155.88	$155.90	$155.90
Purchase #6	$58.98	8.343%	$63.9007	$63.90	$63.90	$63.90
Purchase #7	$41.48	13.517%	$47.0869	$47.09	$47.10	$47.10
7 purchase totals =	$660.74		$735.8918	$735.88	$735.90	$736.00