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	$79.36	4.652%	$83.0518	$83.05	$83.05	$83.10
Purchase #2	$13.53	11.638%	$15.1046	$15.10	$15.10	$15.10
Purchase #3	$59.88	12.321%	$67.2578	$67.26	$67.25	$67.30
Purchase #4	$7.32	5.676%	$7.7355	$7.74	$7.75	$7.70
Purchase #5	$128.27	9.105%	$139.949	$139.95	$139.95	$139.90
Purchase #6	$42.62	6.192%	$45.259	$45.26	$45.25	$45.30
Purchase #7	$68.72	3.330%	$71.0084	$71.01	$71.00	$71.00
7 purchase totals =	$399.70		$429.3661	$429.37	$429.35	$429.40