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	$35.31	3.268%	$36.4639	$36.46	$36.45	$36.50
Purchase #2	$33.78	9.821%	$37.0975	$37.10	$37.10	$37.10
Purchase #3	$226.83	10.268%	$250.1209	$250.12	$250.10	$250.10
Purchase #4	$135.49	4.512%	$141.6033	$141.60	$141.60	$141.60
Purchase #5	$82.41	11.731%	$92.0775	$92.08	$92.10	$92.10
Purchase #6	$203.97	13.555%	$231.6181	$231.62	$231.60	$231.60
Purchase #7	$35.70	12.705%	$40.2357	$40.24	$40.25	$40.20
7 purchase totals =	$753.49		$829.2169	$829.22	$829.20	$829.20