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	$7.47	12.797%	$8.4259	$8.43	$8.45	$8.40
Purchase #2	$216.72	8.155%	$234.3935	$234.39	$234.40	$234.40
Purchase #3	$202.81	6.524%	$216.0413	$216.04	$216.05	$216.00
Purchase #4	$39.96	7.337%	$42.8919	$42.89	$42.90	$42.90
Purchase #5	$81.52	13.576%	$92.5872	$92.59	$92.60	$92.60
Purchase #6	$113.82	13.179%	$128.8203	$128.82	$128.80	$128.80
Purchase #7	$82.56	8.688%	$89.7328	$89.73	$89.75	$89.70
7 purchase totals =	$744.86		$812.8929	$812.89	$812.95	$812.80