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	$86.35	4.760%	$90.4603	$90.46	$90.45	$90.50
Purchase #2	$218.63	5.582%	$230.8339	$230.83	$230.85	$230.80
Purchase #3	$30.33	8.358%	$32.865	$32.87	$32.85	$32.90
Purchase #4	$25.90	9.842%	$28.4491	$28.45	$28.45	$28.40
Purchase #5	$141.57	13.273%	$160.3606	$160.36	$160.35	$160.40
Purchase #6	$238.52	10.241%	$262.9468	$262.95	$262.95	$262.90
Purchase #7	$39.84	5.405%	$41.9934	$41.99	$42.00	$42.00
7 purchase totals =	$781.14		$847.9091	$847.91	$847.90	$847.90