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	$102.84	10.391%	$113.5261	$113.53	$113.55	$113.50
Purchase #2	$17.65	10.763%	$19.5497	$19.55	$19.55	$19.50
Purchase #3	$144.53	9.586%	$158.3846	$158.38	$158.40	$158.40
Purchase #4	$82.50	8.231%	$89.2906	$89.29	$89.30	$89.30
Purchase #5	$98.74	6.267%	$104.928	$104.93	$104.95	$104.90
Purchase #6	$198.57	13.769%	$225.9111	$225.91	$225.90	$225.90
Purchase #7	$97.37	13.283%	$110.3037	$110.30	$110.30	$110.30
7 purchase totals =	$742.20		$821.8938	$821.89	$821.95	$821.80