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	$203.87	12.400%	$229.1499	$229.15	$229.15	$229.10
Purchase #2	$134.40	9.770%	$147.5309	$147.53	$147.55	$147.50
Purchase #3	$233.98	9.704%	$256.6854	$256.69	$256.70	$256.70
Purchase #4	$59.88	3.556%	$62.0093	$62.01	$62.00	$62.00
Purchase #5	$175.61	10.726%	$194.4459	$194.45	$194.45	$194.40
Purchase #6	$63.78	11.401%	$71.0516	$71.05	$71.05	$71.10
Purchase #7	$154.59	7.131%	$165.6138	$165.61	$165.60	$165.60
7 purchase totals =	$1,026.11		$1,126.4868	$1,126.49	$1,126.50	$1,126.40