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	$132.89	5.584%	$140.3106	$140.31	$140.30	$140.30
Purchase #2	$154.32	9.679%	$169.2566	$169.26	$169.25	$169.30
Purchase #3	$109.48	10.483%	$120.9568	$120.96	$120.95	$121.00
Purchase #4	$44.83	11.561%	$50.0128	$50.01	$50.00	$50.00
Purchase #5	$131.35	9.293%	$143.5564	$143.56	$143.55	$143.60
Purchase #6	$19.98	4.744%	$20.9279	$20.93	$20.95	$20.90
Purchase #7	$78.76	8.305%	$85.301	$85.30	$85.30	$85.30
7 purchase totals =	$671.61		$730.3221	$730.33	$730.30	$730.40