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	$143.90	4.579%	$150.4892	$150.49	$150.50	$150.50
Purchase #2	$34.59	11.175%	$38.4554	$38.46	$38.45	$38.50
Purchase #3	$87.46	3.112%	$90.1818	$90.18	$90.20	$90.20
Purchase #4	$153.96	6.173%	$163.464	$163.46	$163.45	$163.50
Purchase #5	$190.34	11.810%	$212.8192	$212.82	$212.80	$212.80
Purchase #6	$68.72	3.481%	$71.1121	$71.11	$71.10	$71.10
Purchase #7	$28.31	10.199%	$31.1973	$31.20	$31.20	$31.20
7 purchase totals =	$707.28		$757.7190	$757.72	$757.70	$757.80