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	$6.59	11.647%	$7.3575	$7.36	$7.35	$7.40
Purchase #2	$169.61	9.865%	$186.342	$186.34	$186.35	$186.30
Purchase #3	$100.90	3.682%	$104.6151	$104.62	$104.60	$104.60
Purchase #4	$55.75	5.448%	$58.7873	$58.79	$58.80	$58.80
Purchase #5	$85.51	10.312%	$94.3278	$94.33	$94.35	$94.30
Purchase #6	$79.73	11.702%	$89.06	$89.06	$89.05	$89.10
Purchase #7	$21.89	11.227%	$24.3476	$24.35	$24.35	$24.30
7 purchase totals =	$519.98		$564.8373	$564.85	$564.85	$564.80