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	$31.67	6.105%	$33.6035	$33.60	$33.60	$33.60
Purchase #2	$17.73	3.402%	$18.3332	$18.33	$18.35	$18.30
Purchase #3	$245.48	5.266%	$258.407	$258.41	$258.40	$258.40
Purchase #4	$197.90	10.531%	$218.7408	$218.74	$218.75	$218.70
Purchase #5	$235.39	11.795%	$263.1543	$263.15	$263.15	$263.20
Purchase #6	$141.98	5.823%	$150.2475	$150.25	$150.25	$150.20
Purchase #7	$147.63	6.278%	$156.8982	$156.90	$156.90	$156.90
7 purchase totals =	$1,017.78		$1,099.3845	$1,099.38	$1,099.40	$1,099.30