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	$5.72	13.446%	$6.4891	$6.49	$6.50	$6.50
Purchase #2	$49.81	11.483%	$55.5297	$55.53	$55.55	$55.50
Purchase #3	$195.48	5.496%	$206.2236	$206.22	$206.20	$206.20
Purchase #4	$141.28	13.740%	$160.6919	$160.69	$160.70	$160.70
Purchase #5	$139.89	7.328%	$150.1411	$150.14	$150.15	$150.10
Purchase #6	$244.36	12.622%	$275.2031	$275.20	$275.20	$275.20
Purchase #7	$119.47	3.689%	$123.8772	$123.88	$123.90	$123.90
7 purchase totals =	$896.01		$978.1557	$978.15	$978.20	$978.10