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	$49.53	12.359%	$55.6514	$55.65	$55.65	$55.70
Purchase #2	$88.77	4.516%	$92.7789	$92.78	$92.80	$92.80
Purchase #3	$249.96	12.487%	$281.1725	$281.17	$281.15	$281.20
Purchase #4	$153.41	10.673%	$169.7834	$169.78	$169.80	$169.80
Purchase #5	$137.59	10.270%	$151.7205	$151.72	$151.70	$151.70
Purchase #6	$164.48	3.412%	$170.0921	$170.09	$170.10	$170.10
Purchase #7	$159.43	5.809%	$168.6913	$168.69	$168.70	$168.70
7 purchase totals =	$1,003.17		$1,089.8901	$1,089.88	$1,089.90	$1,090.00