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	$82.86	9.863%	$91.0325	$91.03	$91.05	$91.00
Purchase #2	$48.37	9.345%	$52.8902	$52.89	$52.90	$52.90
Purchase #3	$178.61	9.732%	$195.9923	$195.99	$196.00	$196.00
Purchase #4	$156.90	10.213%	$172.9242	$172.92	$172.90	$172.90
Purchase #5	$118.85	10.445%	$131.2639	$131.26	$131.25	$131.30
Purchase #6	$194.54	8.502%	$211.0798	$211.08	$211.10	$211.10
Purchase #7	$132.38	7.787%	$142.6884	$142.69	$142.70	$142.70
7 purchase totals =	$912.51		$997.8713	$997.86	$997.90	$997.90