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	$38.52	11.338%	$42.8874	$42.89	$42.90	$42.90
Purchase #2	$148.45	6.124%	$157.5411	$157.54	$157.55	$157.50
Purchase #3	$116.44	13.117%	$131.7134	$131.71	$131.70	$131.70
Purchase #4	$163.57	13.428%	$185.5342	$185.53	$185.55	$185.50
Purchase #5	$125.63	9.378%	$137.4116	$137.41	$137.40	$137.40
Purchase #6	$164.63	3.210%	$169.9146	$169.91	$169.90	$169.90
Purchase #7	$245.40	11.475%	$273.5597	$273.56	$273.55	$273.60
7 purchase totals =	$1,002.64		$1,098.5620	$1,098.55	$1,098.55	$1,098.50