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	$126.56	13.450%	$143.5823	$143.58	$143.60	$143.60
Purchase #2	$35.86	12.445%	$40.3228	$40.32	$40.30	$40.30
Purchase #3	$228.46	8.361%	$247.5615	$247.56	$247.55	$247.60
Purchase #4	$162.64	3.498%	$168.3291	$168.33	$168.35	$168.30
Purchase #5	$69.29	4.331%	$72.2909	$72.29	$72.30	$72.30
Purchase #6	$201.37	9.368%	$220.2343	$220.23	$220.25	$220.20
Purchase #7	$24.61	10.787%	$27.2647	$27.26	$27.25	$27.30
7 purchase totals =	$848.79		$919.5856	$919.57	$919.60	$919.60