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	$46.62	11.207%	$51.8447	$51.84	$51.85	$51.80
Purchase #2	$196.59	13.153%	$222.4475	$222.45	$222.45	$222.40
Purchase #3	$243.98	12.352%	$274.1164	$274.12	$274.10	$274.10
Purchase #4	$221.48	3.322%	$228.8376	$228.84	$228.85	$228.80
Purchase #5	$220.27	13.847%	$250.7708	$250.77	$250.75	$250.80
Purchase #6	$26.36	7.429%	$28.3183	$28.32	$28.30	$28.30
Purchase #7	$22.82	10.818%	$25.2887	$25.29	$25.30	$25.30
7 purchase totals =	$978.12		$1,081.6240	$1,081.63	$1,081.60	$1,081.50