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	$220.59	13.568%	$250.5197	$250.52	$250.50	$250.50
Purchase #2	$148.96	10.707%	$164.9091	$164.91	$164.90	$164.90
Purchase #3	$73.52	12.161%	$82.4608	$82.46	$82.45	$82.50
Purchase #4	$100.29	8.732%	$109.0473	$109.05	$109.05	$109.00
Purchase #5	$129.51	10.724%	$143.3987	$143.40	$143.40	$143.40
Purchase #6	$229.26	7.489%	$246.4293	$246.43	$246.45	$246.40
Purchase #7	$45.60	11.384%	$50.7911	$50.79	$50.80	$50.80
7 purchase totals =	$947.73		$1,047.5560	$1,047.56	$1,047.55	$1,047.50