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	$87.67	12.589%	$98.7068	$98.71	$98.70	$98.70
Purchase #2	$213.74	3.532%	$221.2893	$221.29	$221.30	$221.30
Purchase #3	$58.52	13.273%	$66.2874	$66.29	$66.30	$66.30
Purchase #4	$35.80	3.614%	$37.0938	$37.09	$37.10	$37.10
Purchase #5	$88.82	4.502%	$92.8187	$92.82	$92.80	$92.80
Purchase #6	$111.62	7.854%	$120.3866	$120.39	$120.40	$120.40
Purchase #7	$174.42	4.520%	$182.3038	$182.30	$182.30	$182.30
7 purchase totals =	$770.59		$818.8864	$818.89	$818.90	$818.90