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	$16.81	8.854%	$18.2984	$18.30	$18.30	$18.30
Purchase #2	$112.30	10.331%	$123.9017	$123.90	$123.90	$123.90
Purchase #3	$32.77	9.675%	$35.9405	$35.94	$35.95	$35.90
Purchase #4	$203.95	3.657%	$211.4085	$211.41	$211.40	$211.40
Purchase #5	$124.25	11.326%	$138.3226	$138.32	$138.30	$138.30
Purchase #6	$128.39	8.378%	$139.1465	$139.15	$139.15	$139.10
Purchase #7	$37.31	8.645%	$40.5354	$40.54	$40.55	$40.50
7 purchase totals =	$655.78		$707.5536	$707.56	$707.55	$707.40