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	$92.25	7.664%	$99.32	$99.32	$99.30	$99.30
Purchase #2	$225.42	6.803%	$240.7553	$240.76	$240.75	$240.80
Purchase #3	$51.55	11.481%	$57.4685	$57.47	$57.45	$57.50
Purchase #4	$51.44	10.546%	$56.8649	$56.86	$56.85	$56.90
Purchase #5	$148.75	11.525%	$165.8934	$165.89	$165.90	$165.90
Purchase #6	$18.47	11.347%	$20.5658	$20.57	$20.55	$20.60
Purchase #7	$16.90	6.603%	$18.0159	$18.02	$18.00	$18.00
7 purchase totals =	$604.78		$658.8838	$658.89	$658.80	$659.00