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	$17.45	8.107%	$18.8647	$18.86	$18.85	$18.90
Purchase #2	$161.28	4.254%	$168.1409	$168.14	$168.15	$168.10
Purchase #3	$155.98	8.740%	$169.6127	$169.61	$169.60	$169.60
Purchase #4	$30.56	3.424%	$31.6064	$31.61	$31.60	$31.60
Purchase #5	$208.97	8.799%	$227.3573	$227.36	$227.35	$227.40
Purchase #6	$92.60	8.341%	$100.3238	$100.32	$100.30	$100.30
Purchase #7	$78.76	8.729%	$85.635	$85.64	$85.65	$85.60
7 purchase totals =	$745.60		$801.5408	$801.54	$801.50	$801.50