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	$135.36	7.356%	$145.3171	$145.32	$145.30	$145.30
Purchase #2	$156.67	8.207%	$169.5279	$169.53	$169.55	$169.50
Purchase #3	$82.97	9.123%	$90.5394	$90.54	$90.55	$90.50
Purchase #4	$234.63	12.867%	$264.8198	$264.82	$264.80	$264.80
Purchase #5	$58.30	11.189%	$64.8232	$64.82	$64.80	$64.80
Purchase #6	$6.72	5.171%	$7.0675	$7.07	$7.05	$7.10
Purchase #7	$100.85	4.486%	$105.3741	$105.37	$105.35	$105.40
7 purchase totals =	$775.50		$847.4690	$847.47	$847.40	$847.40