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	$178.34	5.610%	$188.3449	$188.34	$188.35	$188.30
Purchase #2	$35.42	13.217%	$40.1015	$40.10	$40.10	$40.10
Purchase #3	$119.75	10.629%	$132.4782	$132.48	$132.50	$132.50
Purchase #4	$52.91	12.474%	$59.51	$59.51	$59.50	$59.50
Purchase #5	$178.35	5.556%	$188.2591	$188.26	$188.25	$188.30
Purchase #6	$86.76	13.324%	$98.3199	$98.32	$98.30	$98.30
Purchase #7	$83.47	3.576%	$86.4549	$86.45	$86.45	$86.50
7 purchase totals =	$735.00		$793.4685	$793.46	$793.45	$793.50