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	$117.34	9.489%	$128.4744	$128.47	$128.45	$128.50
Purchase #2	$51.89	4.439%	$54.1934	$54.19	$54.20	$54.20
Purchase #3	$40.75	8.726%	$44.3058	$44.31	$44.30	$44.30
Purchase #4	$125.31	13.565%	$142.3083	$142.31	$142.30	$142.30
Purchase #5	$91.81	11.715%	$102.5655	$102.57	$102.55	$102.60
Purchase #6	$85.97	11.798%	$96.1127	$96.11	$96.10	$96.10
Purchase #7	$151.57	13.360%	$171.8198	$171.82	$171.80	$171.80
7 purchase totals =	$664.64		$739.7799	$739.78	$739.70	$739.80