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	$99.37	13.663%	$112.9469	$112.95	$112.95	$112.90
Purchase #2	$132.41	6.104%	$140.4923	$140.49	$140.50	$140.50
Purchase #3	$233.96	9.666%	$256.5746	$256.57	$256.55	$256.60
Purchase #4	$167.50	7.398%	$179.8917	$179.89	$179.90	$179.90
Purchase #5	$81.87	9.472%	$89.6247	$89.62	$89.60	$89.60
Purchase #6	$32.34	10.448%	$35.7189	$35.72	$35.70	$35.70
Purchase #7	$98.45	13.499%	$111.7398	$111.74	$111.75	$111.70
7 purchase totals =	$845.90		$926.9889	$926.98	$926.95	$926.90