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	$89.51	9.790%	$98.273	$98.27	$98.25	$98.30
Purchase #2	$57.93	11.134%	$64.3799	$64.38	$64.40	$64.40
Purchase #3	$170.25	12.576%	$191.6606	$191.66	$191.65	$191.70
Purchase #4	$78.53	3.166%	$81.0163	$81.02	$81.00	$81.00
Purchase #5	$156.90	5.127%	$164.9443	$164.94	$164.95	$164.90
Purchase #6	$74.86	7.191%	$80.2432	$80.24	$80.25	$80.20
Purchase #7	$45.98	5.407%	$48.4661	$48.47	$48.45	$48.50
7 purchase totals =	$673.96		$728.9834	$728.98	$728.95	$729.00