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	$123.54	4.820%	$129.4946	$129.49	$129.50	$129.50
Purchase #2	$62.50	10.308%	$68.9425	$68.94	$68.95	$68.90
Purchase #3	$75.89	5.753%	$80.256	$80.26	$80.25	$80.30
Purchase #4	$124.81	5.659%	$131.873	$131.87	$131.85	$131.90
Purchase #5	$83.96	12.634%	$94.5675	$94.57	$94.55	$94.60
Purchase #6	$225.49	10.371%	$248.8756	$248.88	$248.90	$248.90
Purchase #7	$218.34	4.375%	$227.8924	$227.89	$227.90	$227.90
7 purchase totals =	$914.53		$981.9016	$981.90	$981.90	$982.00