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	$34.61	7.823%	$37.3175	$37.32	$37.30	$37.30
Purchase #2	$213.96	13.807%	$243.5015	$243.50	$243.50	$243.50
Purchase #3	$75.27	6.669%	$80.2898	$80.29	$80.30	$80.30
Purchase #4	$230.58	8.332%	$249.7919	$249.79	$249.80	$249.80
Purchase #5	$210.26	13.225%	$238.0669	$238.07	$238.05	$238.10
Purchase #6	$134.70	8.299%	$145.8788	$145.88	$145.90	$145.90
Purchase #7	$80.73	12.165%	$90.5508	$90.55	$90.55	$90.60
7 purchase totals =	$980.11		$1,085.3972	$1,085.40	$1,085.40	$1,085.50