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	$36.28	3.464%	$37.5367	$37.54	$37.55	$37.50
Purchase #2	$98.36	13.662%	$111.7979	$111.80	$111.80	$111.80
Purchase #3	$238.83	3.874%	$248.0823	$248.08	$248.10	$248.10
Purchase #4	$134.38	11.802%	$150.2395	$150.24	$150.25	$150.20
Purchase #5	$177.97	7.265%	$190.8995	$190.90	$190.90	$190.90
Purchase #6	$247.42	10.450%	$273.2754	$273.28	$273.30	$273.30
Purchase #7	$76.60	13.511%	$86.9494	$86.95	$86.95	$86.90
7 purchase totals =	$1,009.84		$1,098.7807	$1,098.79	$1,098.85	$1,098.70