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	$69.76	10.863%	$77.338	$77.34	$77.35	$77.30
Purchase #2	$54.52	7.464%	$58.5894	$58.59	$58.60	$58.60
Purchase #3	$90.74	8.569%	$98.5155	$98.52	$98.50	$98.50
Purchase #4	$150.42	12.200%	$168.7712	$168.77	$168.75	$168.80
Purchase #5	$73.71	12.186%	$82.6923	$82.69	$82.70	$82.70
Purchase #6	$79.50	4.117%	$82.773	$82.77	$82.75	$82.80
Purchase #7	$38.25	7.874%	$41.2618	$41.26	$41.25	$41.30
7 purchase totals =	$556.90		$609.9412	$609.94	$609.90	$610.00