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	$237.38	13.857%	$270.2737	$270.27	$270.25	$270.30
Purchase #2	$203.64	9.307%	$222.5928	$222.59	$222.60	$222.60
Purchase #3	$212.33	12.816%	$239.5422	$239.54	$239.55	$239.50
Purchase #4	$125.82	4.682%	$131.7109	$131.71	$131.70	$131.70
Purchase #5	$99.55	11.625%	$111.1227	$111.12	$111.10	$111.10
Purchase #6	$160.84	3.567%	$166.5772	$166.58	$166.60	$166.60
Purchase #7	$96.42	3.238%	$99.5421	$99.54	$99.55	$99.50
7 purchase totals =	$1,135.98		$1,241.3616	$1,241.35	$1,241.35	$1,241.30