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	$191.59	7.140%	$205.2695	$205.27	$205.25	$205.30
Purchase #2	$152.54	12.753%	$171.9934	$171.99	$172.00	$172.00
Purchase #3	$110.44	6.749%	$117.8936	$117.89	$117.90	$117.90
Purchase #4	$56.71	4.709%	$59.3805	$59.38	$59.40	$59.40
Purchase #5	$187.30	12.120%	$210.0008	$210.00	$210.00	$210.00
Purchase #6	$121.27	13.301%	$137.4001	$137.40	$137.40	$137.40
Purchase #7	$124.27	10.392%	$137.1841	$137.18	$137.20	$137.20
7 purchase totals =	$944.12		$1,039.1220	$1,039.11	$1,039.15	$1,039.20