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	$131.60	6.579%	$140.258	$140.26	$140.25	$140.30
Purchase #2	$57.75	11.872%	$64.6061	$64.61	$64.60	$64.60
Purchase #3	$46.60	9.730%	$51.1342	$51.13	$51.15	$51.10
Purchase #4	$157.48	3.444%	$162.9036	$162.90	$162.90	$162.90
Purchase #5	$166.87	11.183%	$185.5311	$185.53	$185.55	$185.50
Purchase #6	$128.36	9.560%	$140.6312	$140.63	$140.65	$140.60
Purchase #7	$100.37	11.401%	$111.8132	$111.81	$111.80	$111.80
7 purchase totals =	$789.03		$856.8774	$856.87	$856.90	$856.80