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	$53.60	7.313%	$57.5198	$57.52	$57.50	$57.50
Purchase #2	$39.92	7.590%	$42.9499	$42.95	$42.95	$42.90
Purchase #3	$25.67	8.198%	$27.7744	$27.77	$27.75	$27.80
Purchase #4	$168.48	10.196%	$185.6582	$185.66	$185.65	$185.70
Purchase #5	$108.43	13.473%	$123.0388	$123.04	$123.05	$123.00
Purchase #6	$176.41	13.215%	$199.7226	$199.72	$199.70	$199.70
Purchase #7	$200.57	11.188%	$223.0098	$223.01	$223.00	$223.00
7 purchase totals =	$773.08		$859.6735	$859.67	$859.60	$859.60