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	$89.89	3.150%	$92.7215	$92.72	$92.70	$92.70
Purchase #2	$122.59	6.508%	$130.5682	$130.57	$130.55	$130.60
Purchase #3	$50.85	11.305%	$56.5986	$56.60	$56.60	$56.60
Purchase #4	$246.31	8.517%	$267.2882	$267.29	$267.30	$267.30
Purchase #5	$171.52	13.426%	$194.5483	$194.55	$194.55	$194.50
Purchase #6	$33.93	9.535%	$37.1652	$37.17	$37.15	$37.20
Purchase #7	$174.48	7.218%	$187.074	$187.07	$187.05	$187.10
7 purchase totals =	$889.57		$965.9640	$965.97	$965.90	$966.00