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	$186.92	12.170%	$209.6682	$209.67	$209.65	$209.70
Purchase #2	$168.60	8.144%	$182.3308	$182.33	$182.35	$182.30
Purchase #3	$111.58	10.402%	$123.1866	$123.19	$123.20	$123.20
Purchase #4	$243.58	5.660%	$257.3666	$257.37	$257.35	$257.40
Purchase #5	$243.60	4.579%	$254.7544	$254.75	$254.75	$254.80
Purchase #6	$80.81	11.258%	$89.9076	$89.91	$89.90	$89.90
Purchase #7	$156.89	12.711%	$176.8323	$176.83	$176.85	$176.80
7 purchase totals =	$1,191.98		$1,294.0465	$1,294.05	$1,294.05	$1,294.10