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	$81.55	13.230%	$92.3391	$92.34	$92.35	$92.30
Purchase #2	$96.57	9.646%	$105.8851	$105.89	$105.90	$105.90
Purchase #3	$213.65	11.459%	$238.1322	$238.13	$238.15	$238.10
Purchase #4	$47.41	11.445%	$52.8361	$52.84	$52.85	$52.80
Purchase #5	$238.75	13.205%	$270.2769	$270.28	$270.30	$270.30
Purchase #6	$167.38	9.102%	$182.6149	$182.61	$182.60	$182.60
Purchase #7	$211.94	13.841%	$241.2746	$241.27	$241.25	$241.30
7 purchase totals =	$1,057.25		$1,183.3589	$1,183.36	$1,183.40	$1,183.30