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	$45.27	13.502%	$51.3824	$51.38	$51.40	$51.40
Purchase #2	$76.46	11.309%	$85.1069	$85.11	$85.10	$85.10
Purchase #3	$183.77	12.802%	$207.2962	$207.30	$207.30	$207.30
Purchase #4	$94.44	11.821%	$105.6038	$105.60	$105.60	$105.60
Purchase #5	$168.70	9.297%	$184.384	$184.38	$184.40	$184.40
Purchase #6	$169.96	12.393%	$191.0231	$191.02	$191.00	$191.00
Purchase #7	$156.69	6.643%	$167.0989	$167.10	$167.10	$167.10
7 purchase totals =	$895.29		$991.8953	$991.89	$991.90	$991.90