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	$5.61	13.204%	$6.3507	$6.35	$6.35	$6.40
Purchase #2	$198.99	12.317%	$223.4996	$223.50	$223.50	$223.50
Purchase #3	$137.66	10.201%	$151.7027	$151.70	$151.70	$151.70
Purchase #4	$140.92	12.197%	$158.108	$158.11	$158.10	$158.10
Purchase #5	$223.54	6.822%	$238.7899	$238.79	$238.80	$238.80
Purchase #6	$116.87	3.497%	$120.9569	$120.96	$120.95	$121.00
Purchase #7	$172.89	5.558%	$182.4992	$182.50	$182.50	$182.50
7 purchase totals =	$996.48		$1,081.9070	$1,081.91	$1,081.90	$1,082.00