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	$68.65	5.317%	$72.3001	$72.30	$72.30	$72.30
Purchase #2	$122.47	7.630%	$131.8145	$131.81	$131.80	$131.80
Purchase #3	$220.89	8.871%	$240.4852	$240.49	$240.50	$240.50
Purchase #4	$153.25	12.404%	$172.2591	$172.26	$172.25	$172.30
Purchase #5	$193.31	10.379%	$213.3736	$213.37	$213.35	$213.40
Purchase #6	$7.59	9.548%	$8.3147	$8.31	$8.30	$8.30
Purchase #7	$235.44	7.600%	$253.3334	$253.33	$253.35	$253.30
7 purchase totals =	$1,001.60		$1,091.8806	$1,091.87	$1,091.85	$1,091.90