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	$43.90	3.578%	$45.4707	$45.47	$45.45	$45.50
Purchase #2	$167.79	7.311%	$180.0571	$180.06	$180.05	$180.10
Purchase #3	$175.27	12.169%	$196.5986	$196.60	$196.60	$196.60
Purchase #4	$141.36	5.766%	$149.5108	$149.51	$149.50	$149.50
Purchase #5	$246.57	8.502%	$267.5334	$267.53	$267.55	$267.50
Purchase #6	$127.94	10.221%	$141.0167	$141.02	$141.00	$141.00
Purchase #7	$181.46	9.377%	$198.4755	$198.48	$198.50	$198.50
7 purchase totals =	$1,084.29		$1,178.6628	$1,178.67	$1,178.65	$1,178.70