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	$78.31	6.768%	$83.61	$83.61	$83.60	$83.60
Purchase #2	$165.86	3.343%	$171.4047	$171.40	$171.40	$171.40
Purchase #3	$120.77	9.248%	$131.9388	$131.94	$131.95	$131.90
Purchase #4	$31.51	7.190%	$33.7756	$33.78	$33.80	$33.80
Purchase #5	$73.74	11.449%	$82.1825	$82.18	$82.20	$82.20
Purchase #6	$57.82	8.812%	$62.9151	$62.92	$62.90	$62.90
Purchase #7	$85.92	13.692%	$97.6842	$97.68	$97.70	$97.70
7 purchase totals =	$613.93		$663.5109	$663.51	$663.55	$663.50