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	$45.67	6.866%	$48.8057	$48.81	$48.80	$48.80
Purchase #2	$243.98	13.488%	$276.888	$276.89	$276.90	$276.90
Purchase #3	$73.59	11.541%	$82.083	$82.08	$82.10	$82.10
Purchase #4	$57.78	10.552%	$63.8769	$63.88	$63.90	$63.90
Purchase #5	$185.87	11.338%	$206.9439	$206.94	$206.95	$206.90
Purchase #6	$158.29	13.328%	$179.3869	$179.39	$179.40	$179.40
Purchase #7	$54.31	4.465%	$56.7349	$56.73	$56.75	$56.70
7 purchase totals =	$819.49		$914.7193	$914.72	$914.80	$914.70