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	$148.32	13.853%	$168.8668	$168.87	$168.85	$168.90
Purchase #2	$134.80	8.661%	$146.475	$146.48	$146.50	$146.50
Purchase #3	$119.46	12.303%	$134.1572	$134.16	$134.15	$134.20
Purchase #4	$240.46	13.269%	$272.3666	$272.37	$272.35	$272.40
Purchase #5	$71.67	11.841%	$80.1564	$80.16	$80.15	$80.20
Purchase #6	$167.45	11.537%	$186.7687	$186.77	$186.75	$186.80
Purchase #7	$96.35	6.209%	$102.3324	$102.33	$102.35	$102.30
7 purchase totals =	$978.51		$1,091.1231	$1,091.14	$1,091.10	$1,091.30