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	$178.40	12.455%	$200.6197	$200.62	$200.60	$200.60
Purchase #2	$39.69	11.657%	$44.3167	$44.32	$44.30	$44.30
Purchase #3	$11.40	11.527%	$12.7141	$12.71	$12.70	$12.70
Purchase #4	$51.93	11.228%	$57.7607	$57.76	$57.75	$57.80
Purchase #5	$196.59	13.533%	$223.1945	$223.19	$223.20	$223.20
Purchase #6	$86.91	4.469%	$90.794	$90.79	$90.80	$90.80
Purchase #7	$142.77	12.296%	$160.325	$160.33	$160.35	$160.30
7 purchase totals =	$707.69		$789.7247	$789.72	$789.70	$789.70