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	$25.66	12.734%	$28.9275	$28.93	$28.95	$28.90
Purchase #2	$29.35	10.580%	$32.4552	$32.46	$32.45	$32.50
Purchase #3	$144.67	13.688%	$164.4724	$164.47	$164.45	$164.50
Purchase #4	$199.29	10.623%	$220.4606	$220.46	$220.45	$220.50
Purchase #5	$140.53	10.700%	$155.5667	$155.57	$155.55	$155.60
Purchase #6	$48.88	13.565%	$55.5106	$55.51	$55.50	$55.50
Purchase #7	$85.53	7.109%	$91.6103	$91.61	$91.60	$91.60
7 purchase totals =	$673.91		$749.0033	$749.01	$748.95	$749.10