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	$246.67	6.838%	$263.5373	$263.54	$263.55	$263.50
Purchase #2	$218.53	8.670%	$237.4766	$237.48	$237.50	$237.50
Purchase #3	$53.32	8.704%	$57.961	$57.96	$57.95	$58.00
Purchase #4	$83.50	7.646%	$89.8844	$89.88	$89.90	$89.90
Purchase #5	$171.71	9.227%	$187.5537	$187.55	$187.55	$187.60
Purchase #6	$34.74	9.373%	$37.9962	$38.00	$38.00	$38.00
Purchase #7	$37.74	6.260%	$40.1025	$40.10	$40.10	$40.10
7 purchase totals =	$846.21		$914.5117	$914.51	$914.55	$914.60