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	$147.56	12.365%	$165.8058	$165.81	$165.80	$165.80
Purchase #2	$176.59	6.723%	$188.4621	$188.46	$188.45	$188.50
Purchase #3	$25.96	11.705%	$28.9986	$29.00	$29.00	$29.00
Purchase #4	$51.53	7.701%	$55.4983	$55.50	$55.50	$55.50
Purchase #5	$78.52	11.656%	$87.6723	$87.67	$87.65	$87.70
Purchase #6	$89.31	12.654%	$100.6113	$100.61	$100.60	$100.60
Purchase #7	$105.50	12.718%	$118.9175	$118.92	$118.90	$118.90
7 purchase totals =	$674.97		$745.9659	$745.97	$745.90	$746.00