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	$65.47	10.712%	$72.4831	$72.48	$72.50	$72.50
Purchase #2	$49.35	3.111%	$50.8853	$50.89	$50.90	$50.90
Purchase #3	$110.80	11.738%	$123.8057	$123.81	$123.80	$123.80
Purchase #4	$147.42	10.273%	$162.5645	$162.56	$162.55	$162.60
Purchase #5	$162.81	3.419%	$168.3765	$168.38	$168.40	$168.40
Purchase #6	$154.25	7.718%	$166.155	$166.16	$166.15	$166.20
Purchase #7	$208.80	12.515%	$234.9313	$234.93	$234.95	$234.90
7 purchase totals =	$898.90		$979.2014	$979.21	$979.25	$979.30