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	$242.59	4.376%	$253.2057	$253.21	$253.20	$253.20
Purchase #2	$88.70	3.209%	$91.5464	$91.55	$91.55	$91.50
Purchase #3	$182.56	7.813%	$196.8234	$196.82	$196.80	$196.80
Purchase #4	$178.57	6.579%	$190.3181	$190.32	$190.30	$190.30
Purchase #5	$52.87	9.231%	$57.7504	$57.75	$57.75	$57.80
Purchase #6	$148.88	10.172%	$164.0241	$164.02	$164.00	$164.00
Purchase #7	$144.52	12.112%	$162.0243	$162.02	$162.00	$162.00
7 purchase totals =	$1,038.69		$1,115.6924	$1,115.69	$1,115.60	$1,115.60