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	$137.95	3.383%	$142.6168	$142.62	$142.60	$142.60
Purchase #2	$174.57	12.713%	$196.7631	$196.76	$196.75	$196.80
Purchase #3	$51.93	11.278%	$57.7867	$57.79	$57.80	$57.80
Purchase #4	$131.28	11.119%	$145.877	$145.88	$145.90	$145.90
Purchase #5	$51.56	3.589%	$53.4105	$53.41	$53.40	$53.40
Purchase #6	$85.75	6.698%	$91.4935	$91.49	$91.50	$91.50
Purchase #7	$236.69	3.639%	$245.3031	$245.30	$245.30	$245.30
7 purchase totals =	$869.73		$933.2507	$933.25	$933.25	$933.30