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	$228.31	9.704%	$250.4652	$250.47	$250.45	$250.50
Purchase #2	$85.73	3.591%	$88.8086	$88.81	$88.80	$88.80
Purchase #3	$145.63	9.108%	$158.894	$158.89	$158.90	$158.90
Purchase #4	$240.74	7.510%	$258.8196	$258.82	$258.80	$258.80
Purchase #5	$32.78	13.465%	$37.1938	$37.19	$37.20	$37.20
Purchase #6	$135.91	5.332%	$143.1567	$143.16	$143.15	$143.20
Purchase #7	$104.34	11.545%	$116.3861	$116.39	$116.40	$116.40
7 purchase totals =	$973.44		$1,053.7240	$1,053.73	$1,053.70	$1,053.80