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	$145.61	12.846%	$164.3151	$164.32	$164.30	$164.30
Purchase #2	$215.25	6.150%	$228.4879	$228.49	$228.50	$228.50
Purchase #3	$122.33	6.680%	$130.5016	$130.50	$130.50	$130.50
Purchase #4	$236.80	13.731%	$269.315	$269.32	$269.30	$269.30
Purchase #5	$62.48	9.776%	$68.588	$68.59	$68.60	$68.60
Purchase #6	$97.88	8.266%	$105.9708	$105.97	$105.95	$106.00
Purchase #7	$97.89	12.285%	$109.9158	$109.92	$109.90	$109.90
7 purchase totals =	$978.24		$1,077.0942	$1,077.11	$1,077.05	$1,077.10