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	$212.29	5.666%	$224.3184	$224.32	$224.30	$224.30
Purchase #2	$55.46	7.305%	$59.5114	$59.51	$59.50	$59.50
Purchase #3	$102.26	10.310%	$112.803	$112.80	$112.80	$112.80
Purchase #4	$132.68	6.330%	$141.0786	$141.08	$141.10	$141.10
Purchase #5	$196.53	5.484%	$207.3077	$207.31	$207.30	$207.30
Purchase #6	$142.28	12.370%	$159.88	$159.88	$159.90	$159.90
Purchase #7	$69.55	12.621%	$78.3279	$78.33	$78.35	$78.30
7 purchase totals =	$911.05		$983.2270	$983.23	$983.25	$983.20