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	$98.61	5.373%	$103.9083	$103.91	$103.90	$103.90
Purchase #2	$133.81	9.793%	$146.914	$146.91	$146.90	$146.90
Purchase #3	$124.38	10.176%	$137.0369	$137.04	$137.05	$137.00
Purchase #4	$161.85	12.399%	$181.9178	$181.92	$181.90	$181.90
Purchase #5	$88.89	9.559%	$97.387	$97.39	$97.40	$97.40
Purchase #6	$36.96	8.759%	$40.1973	$40.20	$40.20	$40.20
Purchase #7	$113.91	3.692%	$118.1156	$118.12	$118.10	$118.10
7 purchase totals =	$758.41		$825.4769	$825.49	$825.45	$825.40