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	$19.79	8.711%	$21.5139	$21.51	$21.50	$21.50
Purchase #2	$91.46	3.403%	$94.5724	$94.57	$94.55	$94.60
Purchase #3	$140.82	4.459%	$147.0992	$147.10	$147.10	$147.10
Purchase #4	$128.59	10.355%	$141.9055	$141.91	$141.90	$141.90
Purchase #5	$88.72	12.290%	$99.6237	$99.62	$99.60	$99.60
Purchase #6	$182.89	3.417%	$189.1394	$189.14	$189.15	$189.10
Purchase #7	$168.44	8.572%	$182.8787	$182.88	$182.90	$182.90
7 purchase totals =	$820.71		$876.7328	$876.73	$876.70	$876.70