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	$42.56	4.818%	$44.6105	$44.61	$44.60	$44.60
Purchase #2	$82.63	8.365%	$89.542	$89.54	$89.55	$89.50
Purchase #3	$165.93	6.300%	$176.3836	$176.38	$176.40	$176.40
Purchase #4	$163.53	3.451%	$169.1734	$169.17	$169.15	$169.20
Purchase #5	$54.29	6.518%	$57.8286	$57.83	$57.85	$57.80
Purchase #6	$199.30	12.140%	$223.495	$223.50	$223.50	$223.50
Purchase #7	$216.59	3.794%	$224.8074	$224.81	$224.80	$224.80
7 purchase totals =	$924.83		$985.8405	$985.84	$985.85	$985.80