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	$92.43	6.434%	$98.3769	$98.38	$98.40	$98.40
Purchase #2	$139.99	8.618%	$152.0543	$152.05	$152.05	$152.10
Purchase #3	$88.99	13.430%	$100.9414	$100.94	$100.95	$100.90
Purchase #4	$17.50	7.260%	$18.7705	$18.77	$18.75	$18.80
Purchase #5	$147.94	10.172%	$162.9885	$162.99	$163.00	$163.00
Purchase #6	$249.84	8.292%	$270.5567	$270.56	$270.55	$270.60
Purchase #7	$155.81	12.238%	$174.878	$174.88	$174.90	$174.90
7 purchase totals =	$892.50		$978.5663	$978.57	$978.60	$978.70