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	$17.38	4.281%	$18.124	$18.12	$18.10	$18.10
Purchase #2	$154.82	8.185%	$167.492	$167.49	$167.50	$167.50
Purchase #3	$215.97	11.372%	$240.5301	$240.53	$240.55	$240.50
Purchase #4	$69.55	11.440%	$77.5065	$77.51	$77.50	$77.50
Purchase #5	$86.62	10.407%	$95.6345	$95.63	$95.65	$95.60
Purchase #6	$186.30	9.788%	$204.535	$204.54	$204.55	$204.50
Purchase #7	$55.32	3.853%	$57.4515	$57.45	$57.45	$57.50
7 purchase totals =	$785.96		$861.2736	$861.27	$861.30	$861.20